Fractions of konjac glucomannan (KGM) with various viscosity-average molecular weights (M-v) ranging from 4.00 x 10(5) to 2.50 x 10(6) were prepared by hydrolysis degradation in hydrochloride acid/ethanol. Effect of M-v of KGM on the critical gelation temperature (T-gel) determined by Winter-Chambon criterion and the elasticity of KGM/xanthan mixed gels, a kind of binary gel formed by synergistic gelation, were investigated by dynamic viscoelastic measurements. It was shown that the value of T-gel of the gel was shifted to a higher temperature and the gel strength was enhanced when M-v of KGM was increased. The critical M-v (1.91 x 10(6)) was observed, above which the T-gel and elasticity of the mixed gels showed no or slight increase. It was suggested that T-gel, and elasticity of KGM/xanthan mixed gels mainly depend on the structure of junction zones driven by the strong interaction between KGM and xanthan, which was gradually improved with increasing M-v of KGM. It was found that the critical strain and yield stress of the mixed gels increased monotonically with the increasing M-v of KGM. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 313-321, 2010