Because of the transesterifiction reaction between poly(butylene terephthalate) (PBT) and polycarbonate (PC) , the crystallization behavior and thermal-resistant Properties of the blend have been known to be decreased. Therefore it is of importance to control the transesterification degree in PBT/PC blends. In this article, the effect of silicone Phosphate on the transesterification reaction between PBT and PC was studied using differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), and infrared spectroscopy (IR). It was found that the crystallization temperature of PBT/PC/silicone phosphate was 18.0 degrees C than that of pure system, and the difference of the crystallization temperature between the first and secondary cooling cycles in DSC was 15.8 degrees C lower than that of the pure system. IR results showed that both random and block copolymer existed in the stabilized system,and both IR and NMR results proved the decrease of the copolymer content by the introduction of silicone phosphate. Compared with that of the pure system, the vicat soft temperature of the stabilized system was increased by 17.2 degrees C. All the showed that silicone phosphate was an effective inhibitor for the controlling of the transesterification reaction in PBT/PC blends. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 87-95, 2009