This article focuses on why and how the chemical synthesis of cellulose was accomplished. The synthesis of cellulose was an important, challenging problem for half a century in polymer chemistry. For the synthesis, a new method of enzymatic polymerization was developed. A monomer of P-D-cellobiosyl fluoride (beta-CF) was designed and subjected to cellulase catalysis, which led to synthetic cellulose for the first time. Cellulase is a hydrolysis enzyme of cellulose:. cellulase, inherently catalyzing the bond cleavage of cellulose in vivo, catalyzes the bond formation via the polycondensation of beta-CF in vitro. It is thought that the polymerization and hydrolysis involve a common intermediate (transition state). This view led us to a new concept, a transition-state analogue substrate. for the design of the monomer. The preparation of cellulase proteins with biotechnology revealed die enzymatic catalytic functions in the hydrolysis and polymerization to cellulose. High-order molecular structures were in situ formed and observed as fibrils (cellulose 1) and spherulites (cellulose 11). In sini small-angle neutron scattering measurements suggested a fractal surface formation of a synthetic cellulose assembly. The principle of cellulose synthesis was extended to the synthesis of other natural polvsaccharides. such as xylan and amylose. and unnatural polysaccharides. (C) 2004 Wiley periodicals, Inc.