Carbonated soybean oil (CSBO) can be used as intermediate for the synthesis of non-isocyanate polyurethanes (NIPUs). In this work, CSBO was prepared by the reaction of epoxidized soybean oil (ESBO) with carbon dioxide (CO2) using a novel composite catalyst comprising SnCl4 center dot 5H(2)O and tetrabutylammonium bromide (TBABr). The evolution of the reaction process and structure of CSBO were studied by means of IR, H-1-NMR, and GPC techniques. Effects of catalyst formulation and various reaction conditions on the reaction were examined. The results showed that the obvious improvement in ESBO conversion using the present composite catalyst under mild conditions was achieved. Moreover, it was interesting to note that very high purity of CSBO was not a prerequisite for the synthesis of NIPUs with good performance.