The present invention relates to a manufacturing method for an organopolysiloxane-polyoxyalkylene block copolymer obtained by condensation reaction of a polyoxyalkylene compound having a particular chemical structure and an organopolysiloxane having a particular chemical structure. The manufacturing method according to the present invention can enable an easy manufacturing of a high molecular weight organopolysiloxane-polyoxyalkylene block copolymer and provide an organopolysiloxane-polyoxyalkylene block copolymer where an amount of volatile cyclic polysiloxane produced as a by-product is small.
