To obtain a desired product in a high yield by hydrosilylating an unsaturated reactant using a specific complex as a catalyst to selectively hydrosilylate the unsaturated organic compound having internal unsaturated bond.

A hydrosilylation is conducted between (A) a silicon hydride of the formula (R1 is a 1-20C alkyl or the like; X is a halogen; (a) is 0-3; (a+b)=1-4) and (B) an unsaturated reactant selected from the group consisting of unsaturated organic compounds, silicon compounds bearing unsaturated organic substituent (s) and mixtures thereof, in the presence of (C) an aminoborane complex of the formula R23NBH3 or phosphineborane complex of the formula R23PBH3 (R2 is a 1-10C alkyl or the like) pref. at a temp. of -10 to 260°C; wherein it is preferable that the component B has internal unsaturated bond, and the molar ratios B/A and B/C are (0.4:1) to (1.6:1) and (25:1) to (1,000:1), respectively.