A room temperature curable organopolysiloxane composition is provided. The composition comprises (I) an organopolysiloxane which is a condensation product of component (A) (an organopolysiloxane comprising R3SiO1/2 unit and SiO4/2 unit and containing 0.02 to 0.12 mol/100 g of hydroxy group bonded to the silicon atom) and component (B) (a diorganopolysiloxane raw rubber having hydroxy group on opposite ends thereof), (II) an organosilane compound having at least 2 hydrolyzable groups bonded to the silicon atom on average per molecule, and/or its partial hydrolytic condensate, (III) a solvent, and (IV) a silica nano particle having its surface modified by a branch structure. The composition is capable of providing a high strength film without incorporating reinforcement fillers, with no curing inhibition by the inorganic nano particles, and without inhibiting gas separation performance realized by the inorganic nano particles.