Syndiotactic polystyrene/highly-impact polystyrene (sPS/HIPS) blends were prepared with a twinscrew extruder. Differential scanning calorimetry and wide angle X-ray diffractometry were used to investigate the effect of the maximal melting temperature, the content of HIPS and cooling rates on the melting and crystallization behavior and crystal forms of sPS. The experimental results indicated that the addition of low content of HIPS induced the formation of more alpha-crystal, whereas the addition of high content of HIPS favored the formation of beta-crystal for SPS/HIPS blends crystallized dynamically from low melting temperature. Both sPS and its blends produced only beta-crystal as crystallized from high melting temperature. The crystallization temperatures of sPS and its blends decreased as the melting temperature increased, favoring the formation of beta-crystal. Higher temperature of sPS crystallization favored the formation of more content of alpha-crystal while lower temperature of sPS crystallization produced more content of beta-crystal. Cooling rates showed no significant effect on the crystal form of sPS and its blends, but influenced the melting behavior of both sPS and its bends. (c) 2006 Wiley Periodicals, Inc.