Liquid polysulfide rubber (LP-3) was used as a toughening modifier to improve the toughness of polybenzoxazine obtained from bisphenol A. aniline based benzoxazine (B-a). The mixing and curing processes of B-a and LP-3 were monitored by H-1. NMR, FTIR and DSC. It was found that the ring. opening addition reaction between B-a and LP-3 happened during mixing, and the resultants showed lower curing temperature and faster curing rate than the pure B-a. The thermal and mechanical properties of the cured materials with various LP-3 incorporations were measured by TGA, DMA, impacting and flexural test. The results showed that LP-3 was an effective toughener for polybenzoxazine from B-a. Materials containing LP-3 in the crosslinked network showed much better toughness than that without LP-3. With the increase of LP-3 incorporation, impacting strength increased while modulus and glass transition temperature (T-g) decreased. When 5 wt% LP-3 was added, the impacting strength of the cured material was about 3.4 times higher than that of the polybenzoxazine from pure B-a. Simultaneously, the material at this LP-3 content retained high storage modulus (E' = 3.9 GPa at 30 degrees C) and high glass transition temperature (T-g = 206 degrees C) with improved flexural properties and thermal stability (T-5% = 322 degrees C, T-10% = 342 degrees C). It was concluded that LP-3 was a promising modifier for the commercial B. a resin even with small addition amount. When the amount of LP-3 was 5 wt%, the cured material owned the best overall performance.