Differential scanning calorimetry (DSC) and X-ray diffraction analysis were performed to study the multiple melting behavior and crystal forms of neat syndiotactic polystyrene (s-PS) in comparison with its miscible blends with amorphous atactic polystyrene (a-PS) or poly(2,6-dimethyl-p-phenylene oxide) (PPO). For neat s-PS annealed at 242 to 25OoC, three melting peaks of changing intensity were observed (labeled I, 11, and I11 from low to high temperature), while if annealed at high temperatures (254Β°C or higher) only two melting peaks were left. The missing peak was determined to be Peak-I11 for s-PS annealed at high temperatures. For the s-PS/a-PS or s-PSPPO blends, two melting peaks were observed, and the missing peak is Peak-11. The missing Peak-I1 in the blend systems is attributed to the a-modification. Apparently, the condition of s-PS being compatible with a-PS or PPO is unfavorable for generating the a-modification upon melt crystallization. This study also showed that Peak-I is associated with the P-modification. Peak-I11 may be associated with the less stable p' form, which can be transformed to the P form upon annealing at high temperatures. For the s-PS/a-PS or s-PSPPO blends upon annealing at higher temperatures, Peak-I11 quickly decreases, leaving only a single melting peak (Peak-I) for the blends. The phenomenon of the decrease of Peak-I11 crystals in the blend is similar to that for neat s-PS annealed at high temperatures.