Poly(ethylene oxide-b-propylene oxide) allyl ether (allyl P(EO-b-PO)) having reactive end group was synthesized by addition reaction of ethylene oxide (EO) and propylene oxide (PO) with allyl alcohol as initiator. Molecular weights and hydrophilic/hydrophobic balance of the block copolymer were controlled by the EO/PO ratios. Reaction conversion, side reaction, molecular weight, and purity of the resulting polymer demonstrated by 1H NMR, FT-IR, and GPC studies.