Both propylene oxide and epichlorohydrin could effectively promote the polymerization of tetrahydrofuran initiated with a heteropolyacid, H3PW12O40, in low concentration. Water or butylene glycol was used to control the molecular weight of the product in the range of 1000-3000. The promotion activity of propylene oxide was similar to that of ethylene oxide and better than that of epichlorohydrin, especially when water was introduced. The polymerization started upon addition of propylene oxide or epichlorohydrin. After the polymerization stopped, it could be reinitiated with the addition of a new portion of propylene oxide or epichlorohydrin. The products were found to be copolyether glycol with hydroxyl groups at both ends. The melting point of the polymer obtained by using propylene oxide promoter was about 20 degrees C lower than that of polytetramethylene ether glycol having the same molecular weight.