Cationic graft copolymerization of tetrahydrofuran onto halodeoxycelluloses, which were prepared under homogeneous conditions, was studied with silver tetrafluoroborate as an initiator. 6-Bromo-6-deoxycelluloses gave graft copolymers, insoluble but swollen in tetrahydrofuran, whereas chlorodeoxycelluloses gave no graft copolymer. The graft copolymers were hydrolyzed in 2N HCI to give hydrolyzate solutions and insoluble solids. The hydrolyzate was found to be composed of 6-0-(4-hydroxybutyl) glucose and 6-0-(9-hydroxy-5-oxanonyl) glucose as well as oligomers of tetrahydrofuran by gas chromatography and gas chromatography-mass spectrometry after trifluoroacetylation. The insoluble solid was cross-linked polyoxytetramethylene, which could be hydrolyzed only very slowly in 2N HCI to yield oligomers of tetrahydrofuran. Thermal behavior of the graft copolymer was compared with that of cellulose and of homopolymer of tetrahydrofuran.