Syndiotactic polystyrene (sPS) delta crystals within atactic polystyrene (aPS) and atactic polystyrene networks (aPSNW) were prepared. The polymorphism behaviors of sPS within aPS and aPSNW were studied by in-situ wide-angle X-ray diffraction (WAXD) and differential scanning calorimeter (DSC). The sPS delta crystals transfer into gamma and then alpha form crystals during the gradually heating process. The transition temperature of the delta to gamma form crystals decreases with the increase in the aPS and aPSNW content in all samples. By contrast, the transition temperature of gamma-to-alpha form crystals increases with the rising aPSNW content, whereas it is independent of the content of aPS. Meanwhile, the transition temperatures of delta to gamma and gamma to a in aPSNW are higher than those in linear aPS blends. When the samples were annealed at a temperature above 150 degrees C, the sPS delta form is not favorable to transform into the beta form in aPSNW. The results indicate that polymorphism behaviors of sPS are disturbed within aPS networks.