Changes in the crystal morphology, crystallinity, and the melting process of thermoplastics resulted in significant changes in the processability and mechanical behavior of composites. In our former study, we prepared a novel antibacterial UHMWPE/CA‐MMT composite. In this study, the crystal process and crystallization kinetics of pure UHMWPE, UHMWPE/MMT, UHMWPE/CA, and UHMWPE/CA‐MMT were characterized by differential scanning calorimeter (DSC). The results showed that the chlorhexidine acetate (CA) and montmorillonite (MMT) could cause strong heterogeneous nucleation. The results of crystallization kinetics indicated that the addition of CA could decrease the crystallization rate constant K value and widen the range of the crystal growth temperature. The reological behaviors of four samples were carried out by a physical MCR301 rheometer. The results showed that the CA could bring down the complex viscosity of composites, thus affecting the crystal process or crystallization kinetics. POLYM. COMPOS., 33:1987–1992, 2012. © 2012 Society of Plastics Engineers