To obtain a block copolymer which is excellent in crumbiness, dehydrability and dryability, and stickiness by subjecting a soln. contg. a block copolymer obtd. by copolymerizing a conjugated diene and an arom. vinyl under specified conditions to steam stripping under specified conditions.

A conjugated diene (e.g. 1,3-butadiene) and an arom. vinyl (e.g. styrene) are copolymerized in a hydrocarbon solvent (e.g. an n-butane/ cyclohexane mixture) by using an active organometal (e.g. n-butyllithium) as the initiator to give a block copolymer. A soln. contg. the block copolymer is subjected to steam stripping in the presence of a cationic surfactant (e.g. cetyltrimethylammonium chlride) pref. in an amt. of 0.00001-10wt.% of the copolymer and an anionic surfactant (e.g. sodium polycarboxylate) pref. in an amt. of 0.001-1.0wt.% of the block copolymer.