An oxytetramethylene glycol copolymer obtained by copolymerizing tetrahydrofuran and neopentyl glycol which has a specific number average molecular weight Mn, a specific molecular weight distribution Mw/Mn, a specific neopentyl glycol copolymerization whole ratio N.sub.w and a specific neopentyl glycol copolymerization partial ratio N.sub.h; a method for producing the same; and a method for purifying an oxytetramethylene glycol copolymer using fresh tetrahydrofuran.