Quantitative double electron reduction of the cationic propagation end of poly(tetrahydrofuran) into a terminating nucleophile was achieved by using samarium(II) iodide in the presence of hexamethylphosphoramide. Termination of the resulting organosamarium group at the terminus of the poly(THF) was attempted by using a variety of typical electrophiles such as aldehydes, ketones, isocyanates, and alkyl halides. The functionality of the obtained poly(THF)s was 0.64-1.10 when aldehydes, ketones, or isocyanates were used as electrophiles, indicating that the reaction of the terminating nucleophile with electrophiles successively proceeded. In the case of using allyl bromide or benzyl bromide as a terminating agent, the functionality of the poly(THF)s decreased (0.11-0.20).