Disclosed is a sPS nanocomposite with improved crystallization properties and higher mechanical strength, which comprises a polymer matrix containing syndiotactic polystyrene (sPS), and a layered clay material uniformly dispersed in the polymer matrix. The layered clay material is intercalated with an organic onium cation and optionally along with a polymer or oligomer which is compatible or partially compatible with sPS. The interlayer distances of the layered clay material are at least 20 .ANG.. The sPS nanocomposite can be prepared by ways of in-situ polymerization, melt blending, or solution blending. According to the invention, the layered clay material dispersed in the sPS matrix not only leads to higher mechanical strength, but also, surprisingly, improves crystallization properties of sPS.