Abstract: It is possible to obtain a porous substrate having a water/oil repellent-treated surface and a moisture-permeable waterproofing film, which has favorable water/oil repellency and wash durability, through which penetration of a coating liquid for formation of the moisture-permeable waterproofing film is suppressed, and from which peeling of the moisture-permeable waterproofing film is suppressed. A water/oil repellent composition comprising a copolymer (A) having from 60 to 95 mass % of units based on a monomer having a RF group having at most 6 carbon atoms and from 5 to 40 mass % of units based on vinylidene chloride, a copolymer (B) having from 50 to 95 mass % of units based on a halogenated olefin and from 5 to 50 mass % of units based on a monomer having a crosslinkable functional group, and a medium (C), wherein the proportion of the copolymer (A) is from 70 to 90 mass %, and the proportion of the copolymer (B) is from 10 to 30 mass %.