A low dielectric constant siliceous film manufacturing composition, comprising: a polysiloxane which comprises a repeating unit represented by the following formula (Ia): wherein R 1 is hydrogen, a monovalent to trivalent, linear, branched or cyclic, saturated or unsaturated C 1-30 aliphatic hydrocarbon group, or a monovalent to trivalent C 6-30 aromatic hydrocarbon group, in said aliphatic hydrocarbon group and said aromatic hydrocarbon group, one or more methylene is unsubstituted or substituted with oxy, imide or carbonyl, one or more hydrogens are unsubstituted or substituted with fluorine, hydroxy or alkoxy, or one or more carbons are unsubstituted or substituted with silicon, when R 1 is divalent or trivalent, R 1 connects Si atoms contained in a plurality of repeating units; and a repeating unit represented by the following formula (Ib): and further which shows a spectrum in which the area intensities S1 and S2 of the peaks in the ranges of 1100±100 cm -1 and 900±100 cm -1 assigned to Si-O and SiOH, respectively, are in a S2/S1 ratio of 0.05 to 0.15 when measured and analyzed by FT-IR, a pore-generating material, a condensation catalyst generator, and a solvent, wherein said pore-generating material is a polycyclic hydrocarbon and the polycyclic hydrocarbon is from 50 to 200 mass% based on the mass of the polysiloxane. a polysiloxane which comprises a repeating unit represented by the following formula (Ia): wherein R 1 is hydrogen, a monovalent to trivalent, linear, branched or cyclic, saturated or unsaturated C 1-30 aliphatic hydrocarbon group, or a monovalent to trivalent C 6-30 aromatic hydrocarbon group, in said aliphatic hydrocarbon group and said aromatic hydrocarbon group, one or more methylene is unsubstituted or substituted with oxy, imide or carbonyl, one or more hydrogens are unsubstituted or substituted with fluorine, hydroxy or alkoxy, or one or more carbons are unsubstituted or substituted with silicon, when R 1 is divalent or trivalent, R 1 connects Si atoms contained in a plurality of repeating units; and a repeating unit represented by the following formula (Ib): and further which shows a spectrum in which the area intensities S1 and S2 of the peaks in the ranges of 1100±100 cm -1 and 900±100 cm -1 assigned to Si-O and SiOH, respectively, are in a S2/S1 ratio of 0.05 to 0.15 when measured and analyzed by FT-IR, R 1 is hydrogen, a monovalent to trivalent, linear, branched or cyclic, saturated or unsaturated C 1-30 aliphatic hydrocarbon group, or a monovalent to trivalent C 6-30 aromatic hydrocarbon group, in said aliphatic hydrocarbon group and said aromatic hydrocarbon group, one or more methylene is unsubstituted or substituted with oxy, imide or carbonyl, one or more hydrogens are unsubstituted or substituted with fluorine, hydroxy or alkoxy, or one or more carbons are unsubstituted or substituted with silicon, when R 1 is divalent or trivalent, R 1 connects Si atoms contained in a plurality of repeating units; and a repeating unit represented by the following formula (Ib): and further which shows a spectrum in which the area intensities S1 and S2 of the peaks in the ranges of 1100±100 cm -1 and 900±100 cm -1 assigned to Si-O and SiOH, respectively, are in a S2/S1 ratio of 0.05 to 0.15 when measured and analyzed by FT-IR, a pore-generating material, a condensation catalyst generator, and a solvent,