To provide a method for manufacturing a block polymer which stably enables narrow molecular weight distribution control and precision molecular weight control even in the polymerization scale of the mass production level, and furthermore inkjet printer aqueous ink containing the block polymer obtained by the above manufacturing method.

The method for manufacturing a block polymer using the living cationic polymerization method comprises a preparatory step of previously preparing a preparatory solution in which a monomer and a polymerization catalyst coexist and a polymerization step of adding a polymerization initiator to the preparatory solution to initiate polymerization. The inkjet printer aqueous ink comprises the block polymer obtained by the above manufacturing method.