To provide a room temperature curable polyorganosiloxane composition which has a low viscosity and fluidity, ensures a low modulus, high elongation, high strength and good adhesion of a cured product thereof, and does not contaminate the surrounding part.

There is provided a method for preparing a room temperature curable polyorganosiloxane composition comprising: 100 parts of (A) a polyorganosiloxane having on average two or more silanol groups and/or ketoxymato groups; 5-100 parts of (B) a polyorganosiloxane having a silanol group or a ketoxymato group; 20-200 parts of (C) calcium carbonate; 0.5-25 parts of (D) a silane compound having a hydrolyzable group; and 0.01-10 parts of (E) a curing catalyst; wherein the component (D) contains 0.05-5.0 parts of (D1) a silane having a mercapto group. The component (D1) is added to a mixture of the component (A), the component (B) and the component (C) before blending the mixture with the other component (D).