An aqueous surface-treating agent, which comprises a silicone oil aqueous emulsion, a polyurethane resin aqueous emulsion, and a silane compound represented by the following general formula (where R1 and R2 each are an alkyl group having 1 to 4 carbon atoms, and n and m are 1≦n≦3 and m=3·n, respectively), and/or a hydrolyzate thereof, wherein 100 parts by weight or more of the polyurethane resin in terms of the weight of solid matters is used on the basis of 100 parts by weight in terms of nonvolatile matters of silicone oil, can prevent sticking of rubber seal materials such as O rings, etc. themselves or sticking to a metal, a resin, etc., and can reduce the friction of rubber or resin seal members at the time of sliding motion.