A π-conjugated polymer composition comprising: (a) a solvent; (b) a π-conjugated polymer which is dissolved in the solvent and doped with a dopant; (c) at least one of an acidic substance and a salt of an acidic substance; and (d) a phenolic compound; wherein the doped π-conjugated polymer is a substituted or unsubstituted polyaniline which is protonated by a sulfonic acid, and the sulfonic acid is a sulfosuccinic acid derivative represented by the following formula: M(O 3 SCH(CH 2 COOR 12)COOR 13) m wherein M is a hydrogen atom, or a inorganic free radical group selected from sodium, lithium, potassium, cesium or ammonium, m is a valency of M; and R 12 and R 13 are independently a hydrocarbon group or a group represented by -(R 14 O) r -R 15 wherein R 14 is a hydrocarbon group or a silylene group, R 15 is a hydrogen atom, a hydrocarbon group or a group represented by R 16 3 Si- wherein R 16 is a hydrocarbon group and three R 16 s may be the same or different, and r is an integer of 1 or more, wherein when only the acidic substance is contained as the component (c), the acidic substance is different from the phenolic compound, when only the salt of an acidic substance is contained as the component (c), the salt of an acidic substance is different from the phenolic compound, and when both the acidic substance and the salt of an acidic substance are contained as the component (c), at least one of the acidic substance and the salt of an acidic substance is different from the phenolic compound, wherein the acidic substance or the salt of an acidic substance is a substituted or unsubstituted aromatic sulfonic acid or polysulfonic acid having one or more sulfonic acid groups, or one or more salts thereof, and wherein the doping ratio a of the doped π-conjugated polymer is 0.2<a<0.7. (a) a solvent; (b) a π-conjugated polymer which is dissolved in the solvent and doped with a dopant; (c) at least one of an acidic substance and a salt of an acidic substance; and (d) a phenolic compound; wherein the doped π-conjugated polymer is a substituted or unsubstituted polyaniline which is protonated by a sulfonic acid, and the sulfonic acid is a sulfosuccinic acid derivative represented by the following formula: M(O 3 SCH(CH 2 COOR 12)COOR 13) m wherein M is a hydrogen atom, or a inorganic free radical group selected from sodium, lithium, potassium, cesium or ammonium, m is a valency of M; and R 12 and R 13 are independently a hydrocarbon group or a group represented by -(R 14 O) r -R 15 wherein R 14 is a hydrocarbon group or a silylene group, R 15 is a hydrogen atom, a hydrocarbon group or a group represented by R 16 3 Si- wherein R 16 is a hydrocarbon group and three R 16 s may be the same or different, and r is an integer of 1 or more, wherein M is a hydrogen atom, or a inorganic free radical group selected from sodium, lithium, potassium, cesium or ammonium, m is a valency of M; and R 12 and R 13 are independently a hydrocarbon group or a group represented by -(R 14 O) r -R 15 wherein R 14 is a hydrocarbon group or a silylene group, R 15 is a hydrogen atom, a hydrocarbon group or a group represented by R 16 3 Si- wherein R 16 is a hydrocarbon group and three R 16 s may be the same or different, and r is an integer of 1 or more, wherein when only the acidic substance is contained as the component (c), the acidic substance is different from the phenolic compound, when only the salt of an acidic substance is contained as the component (c), the salt of an acidic substance is different from the phenolic compound, and when both the acidic substance and the salt of an acidic substance are contained as the component (c), at least one of the acidic substance and the salt of an acidic substance is different from the phenolic compound, wherein the acidic substance or the salt of an acidic substance is a substituted or unsubstituted aromatic sulfonic acid or polysulfonic acid having one or more sulfonic acid groups, or one or more salts thereof, and wherein the doping ratio a of the doped π-conjugated polymer is 0.2<a<0.7.