A binding assay strip comprising: (i) a conjugate release pad that contains a detection reagent that specifically reacts with an analyte, wherein the detection reagent is a labeled antibody, a labeled specific capture substance, or a labeled antigen, and wherein the label is a metal colloid particle, a colored latex particle, horseradish peroxidase, alkaline phosphatase, β-D-galactosidase, iodine-125 ( 125 I), acridinium compounds, luminol, fluorescein isothiocyanate, or a europium chelate; (ii) a blood cell separation pad; and (iii) a porous solid phase for binding assay in which at least one surfactant has been incorporated prior to addition of a test sample, the at least one surfactant being selected from the group consisting of: n-heptyl-β-D-thioglucoside (n-heptyl-β-D-thioglucopyranoside) and n-octyl-β-D-glucoside (n-octyl-β-D-glucopyranoside), wherein the surfactant is immobilized onto the porous solid phase at a concentration of 0.01 to 0.5% (w/v) in the form of a solution and present in a dry state, wherein the surfactant is immobilized at least in a test sample migration area of the porous solid phase which starts at a section to which the test sample is introduced through the conjugate release pad, encompasses a migration path of the test sample, and ends at a section where the capture reagent is immobilized, and optionally, the immobilization of the surfactant extends to the end of the porous solid phase, wherein the surfactant is uniformly immobilized over the test sample migration area of the porous solid phase so that the test sample could migrate evenly, wherein the porous solid phase is a porous membrane, wherein the binding assay is a lateral-flow format or dipstick format membrane assay, wherein a capture reagent that specifically binds to the analyte is immobilized on the porous solid phase, wherein the detection reagent, the analyte and the capture reagent together form a ternary complex on the porous solid phase, and wherein the blood cell separation pad is placed adjacent to the conjugate release pad and the porous solid phase is placed in contact with the other side of the blood cell separation pad. (i) a conjugate release pad that contains a detection reagent that specifically reacts with an analyte, wherein the detection reagent is a labeled antibody, a labeled specific capture substance, or a labeled antigen, and wherein the label is a metal colloid particle, a colored latex particle, horseradish peroxidase, alkaline phosphatase, β-D-galactosidase, iodine-125 ( 125 I), acridinium compounds, luminol, fluorescein isothiocyanate, or a europium chelate; (ii) a blood cell separation pad; and (iii) a porous solid phase for binding assay in which at least one surfactant has been incorporated prior to addition of a test sample, the at least one surfactant being selected from the group consisting of: n-heptyl-β-D-thioglucoside (n-heptyl-β-D-thioglucopyranoside) and n-octyl-β-D-glucoside (n-octyl-β-D-glucopyranoside), wherein the surfactant is immobilized onto the porous solid phase at a concentration of 0.01 to 0.5% (w/v) in the form of a solution and present in a dry state, wherein the surfactant is immobilized at least in a test sample migration area of the porous solid phase which starts at a section to which the test sample is introduced through the conjugate release pad, encompasses a migration path of the test sample, and ends at a section where the capture reagent is immobilized, and optionally, the immobilization of the surfactant extends to the end of the porous solid phase, wherein the surfactant is uniformly immobilized over the test sample migration area of the porous solid phase so that the test sample could migrate evenly, wherein the porous solid phase is a porous membrane, wherein the binding assay is a lateral-flow format or dipstick format membrane assay, wherein a capture reagent that specifically binds to the analyte is immobilized on the porous solid phase, wherein the detection reagent, the analyte and the capture reagent together form a ternary complex on the porous solid phase, and wherein the blood cell separation pad is placed adjacent to the conjugate release pad and the porous solid phase is placed in contact with the other side of the blood cell separation pad. n-heptyl-β-D-thioglucoside (n-heptyl-β-D-thioglucopyranoside) and n-octyl-β-D-glucoside (n-octyl-β-D-glucopyranoside), wherein the surfactant is immobilized onto the porous solid phase at a concentration of 0.01 to 0.5% (w/v) in the form of a solution and present in a dry state, wherein the surfactant is immobilized at least in a test sample migration area of the porous solid phase which starts at a section to which the test sample is introduced through the conjugate release pad, encompasses a migration path of the test sample, and ends at a section where the capture reagent is immobilized, and optionally, the immobilization of the surfactant extends to the end of the porous solid phase, wherein the surfactant is uniformly immobilized over the test sample migration area of the porous solid phase so that the test sample could migrate evenly, wherein the porous solid phase is a porous membrane, wherein the binding assay is a lateral-flow format or dipstick format membrane assay, wherein a capture reagent that specifically binds to the analyte is immobilized on the porous solid phase, wherein the detection reagent, the analyte and the capture reagent together form a ternary complex on the porous solid phase, and wherein the blood cell separation pad is placed adjacent to the conjugate release pad and the porous solid phase is placed in contact with the other side of the blood cell separation pad.