Non-crystalline cellulose (NCC) is a novel product of our laboratory. The crystallinity of NCC is less than 10% and DP is 100-150. Cellulase action on this NCC was found to be very different from crystalline cellulose. Apart from the very high initial hydrolysis rate, NCC also generates cello-olgiosaccharides (COS) as hydrolysis product with cellulase, which are not visible with crystalline cellulose. COS were categorized into two separate fractions: low DP cello-oligosaccharides (LD-COS) and high DP cello-oligosaccharides (HD-COS). LD-COS, from DP 2-7, are detected by HPLC whereas HD-COS are detected only after secondary hydrolysis. On the basis of the profiles of these sugars during enzymatic hydrolysis, individual actions of Exo-glucanase (Exo-G) & Endo-glucanase (Endo-G) are proposed. Other pure cellulosic substrates such as micro-crystalline cellulose (Avicel), á-cellulose, filter paper, cotton are also used in this study. With regard to the reactivity of cellulase, we found that the crystallinity affects the initial rate of cellulose hydrolysis, whereas the DP of cellulose plays an important role in the determination of terminal glucan digestibility. Other findings on the function of individual cellulase components are as follows: (1) Exo-G and Endo-G do not hydrolyze COS. (2) â-G hydrolyzes cellobiose and LD-COS but has negligible reactivity on HD-COS. (3) Reactivity of Exo-G towards the cellulose chain is very low if DP goes below certain value. (4) With NCC, Endo-G mainly works in the beginning of the reaction and produces HD-COS. (5) Reactivity of Endo-G is inversely proportional to the DP of NCC.