Dynamic mechanical analysis (DMA) is an alternative method to chemical techniques in investigating cure processes. However, methods to evaluate mechanical cure state and kinetic analysis for incomplete isothermal curing have not been properly developed. The objective is to find a suitable method to characterize cure state of epoxy prepreg by DMA, and to better understand mechanical incomplete cure processes. Single cantilever mode was applied to the prepreg. A new method was proposed using the dynamic storage modulus data to estimate the core state, and to calculate Ultimate mechanical conversions. Based on this method, the incomplete cure phenomenon was investigated. A linear relationship of the Ultimate mechanical conversions with isothermal temperatures Was observed. Two types of conversion curves were seen at high and low temperatures respectively. The Kamal model with the diffusion effect was filled to the incomplete isothermal mechanical conversion curves, and call well predict the mechanical conversions at high temperatures. (C) 2009 Elsevier B.V. All rights reserved.