Abstract: The isothermal and continuous heating cure processes of a carbon fiber (CF)/bismaleimide (BMI) prepreg were investigated by DMA. Based on the change of dynamic mechanical properties, the criteria for determining the softening, melting, gelation, vitrification transitions and cure reaction points of the prepreg were established, which were confirmed by the measurements of micropolariscope and DSC. The effects of temperature, heating rate and frequency on the transition and reaction points were studied. Maximum mechanical conversions and reaction conversions of isothermal cure processes were measured. The results show that DMA can well detect various transitions and reaction points of the CF/BMI prepreg. Due to the difference in cure reaction mechanism, the variations of the ultimate mechanical and reaction conversions with the isothermal temperature are different below and above 180℃.