Crystallization kinetics and morphology of Poly (ethyleneterephthalate) (PET) containing thermotropic liquid crystalline polyester (LCP) were studied by Differential scanning calorimetry (DSC), Polarized optical microscopy, Scanning electron microscopy and Small-angle light scattering (SALS). Thermotropic liquid crystalline polyester were used to remedy defects of organic and inorganic nucleating agents. Molecular weight of thermotropic polyester was controlled by varying the stoichiometric ratio of reactants. The compositions of thermotropic polyester were fixed at 0.5 and 1.0 weight percent and isothermal crystallization experiments was carried out over the temperature range from 170℃ to 225℃. The half-time of crystallization was decreased by adding liquid crystalline polyester. Because PET with LCP crystallize much faster than pure PET. And high molecular weigh thermotropic polyester had a superior nucleating effectiveness than that of low molecular weight polyester. The crystallization isotherm of pure PET and PET/LCP blend could be characterized with Avrami exponents ranging from 2.64 to 3.60 which suggested the spherical growth of crystalline structure on constant nucleation and sporadic nucleation. Morphology observation by using Polarized optical microscopy and Small-angle light scattering showed that the crystalline structure was spherulite in all case. The size of spherulites was decreased and size distribution was narrowed by adding the thermotropic polyester.