Cellulose, (1-->4)-beta-D-glucopyranan, was for the first time synthesized by cationic ring-opening polymerization of 3,6-di-O-benzyl-alpha-D-glucose 1,2,4-orthopivalate (5) into 3,6-di-O-benzyl-2-O-pivaloyl-beta-D-glucopyranan (6) and subsequent removal of the protective groups. Polymerization of the orthoester 5 by triphenyl carbenium tetrafluoroborate gave 3,6-di-O-benzyl-2-O-pivaloyl-beta-D-glucopyranan with [alpha](D) -37.2 degrees and a number-average molecular weight of 8.3 x 10(3) (DPn = 19.3). Removal of the pivaloyl and benzyl groups and subsequent acetylation gave acetylated (1-->4)-beta-D-glucopyranan which was completely identical with cellulose triacetate (CTA) prepared from low molecular weight cellulose. The synthesized CTA was converted by deacetylation to cellulose, which has the cellulose-II crystal structure.