To provide a medical polyoxypropylene polymer and a polyoxypropylene/polyoxyethylene block copolymer in which an unsaturated ether content is low and the coloring is suppressed. (A) To a polyoxypropylene polymer which is obtained by ring-opening polymerization of propylene oxide to a starting substance having an active hydrogen reacting with the propylene oxide and contains allyl ether as an impurity is added a tertiary alkoxide of alkali metal in an excess amount based on a molar number of the active hydrogen of the starting substance, followed by heat treating at 115°C or less to isomerize the allyl ether to propenyl ether; and (B) to the mixture obtained in the step (A) is added a mineral acid to adjust pH to 4 or less, followed by treating at 70°C or less to hydrolyze the propenyl ether.