RTV organopolysiloxane compositions are provided comprising (A) an organosiloxane polymer comprising R3SiO1/2 units and SiO4/2 units in a molar ratio of 0.6-1.2 wherein R is a monovalent C1-C6 hydrocarbon, and having a hydroxysilyl content of less than 0.04 mole/100 g, (B) a polysiloxane having a hydrolyzable silyl group incorporated in the molecular chain via an alkylene linkage, and (C) a cure catalyst. The compositions have a low viscosity and good workability when heated, develop initial adhesion when allowed to cool after application, and thereafter cure at room temperature and induce crosslinking reaction, affording improved rubber physical properties.