Koniac glucomannan (KGM) is a natural polymer from a plant．It possesses excellent biodegradability

biocompatibility and many unique physiological and pharmacological functions．In this work the effects of various factors (i．e

temperatures

pH

medium) on the activity of β-mannanase was firstly studied．The results show that β-mannanase possesses high activity in the aqueous medium (pH 9.4) containing enthanol less than 5％ (V／V) at about 50℃

and basically lose its activity in the medium with pH lower than 7.0 or containing enthanol more than 20％ (V／V)

or at temperatures lower than 30℃．Based on these results

the degradation reaction of KGM catalyzed by β-mannanase and its affecting factors were investigated

and a series of KGM samples with different molecular weights was prepared by adjusting the reaction conditions．Moreover

the intrinsic viscosity ([η]) and the weight-average molecular weight (Mw) of the degraded KGM products were measured

obtaining the following equation：[η] =5.06×10-4 Mw0.754. This work makes it possible to realize controllable degradation of KGM by means of an enzyme-catalyzed reaction

thus laying a solid experimental and theoretical foundation for further studying the structure and properties of KGM and its derivatives

and developing new application fields of them．