One of the purposes of the present invention is to provide a method for preparing an organopolysiloxane having a short branch chain. In particular, the purposes of the present invention is to provide a method for preparing an organopolysiloxane having a shorter side chain than a main chain, such as a siloxane side chain having 1 to 5 siloxane units. The present preparation methods are characterized in that the starting material is an organosiloxane which is represented by the formula (1) and has two hydrolyzable groups bonded to a silicon atom at one terminal. The present invention provides a method wherein an organo(poly)siloxane represented by the formula (1) is condensation reacted to prepare an organopolysiloxane represented by formula (2) which is then used as starting materials for introducing a branch, whereby a short siloxane side chain is efficiently introduced in the organopolysiloxane, while controlling a structure of the main chain.