To provide a room temperature curing polyorganosiloxane composition which excels in curability, in which strength is high, and from which an adhesive rubber-like cured product excellent in moisture resistance and warm water resistance is obtained.

The composition includes: (A) 100 pts.wt of a polyorganosiloxane in which a molecular chain terminal is blocked by a hydroxy group or a hydrolyzable group, and a viscosity (23°C) is 20-1,000,000 mPa s; (B) 0.1-20 pts.wt of a branched alkyl group containing epoxy compound; (C) 1-400 pts.wt of a filler; and (D) 0.001-10 pts.wt of a curing catalyst. As (B) the branched alkyl group-containing epoxy compound, 2-propyl-2-hexyloxirane, 7,8-epoxy-2-methyloctadecane or the like is mentioned. It is desirable to include (E) an amino alkyl alkoxysilane with the epoxy compound.