A mutant enzyme, EGII(core), in which the cellulose-binding domain was deleted from endoglucanase II from Trichoderma viride, was expressed in yeast, and the secreted enzyme was examined for the enzymatic polymerization to obtain artificial cellulose. EGII(core) polymerized beta-cellobiosyl fluoride to afford crystalline cellulose of type II. Comparison of the polymerization behavior of EGII(core) with that of EGII revealed the following: i) the crystalline product obtained with EGII(core) was stable in the polymerization solution, although the product was readily hydrolyzed in the presence of EGII; ii) the turnover number of EGII(core) was as high as that of EGII; iii) EGII(core) produced highly crystalline cellulose. EGII(core) is therefore advantageous for enzymatic polymerization.