Abstract: An ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS-MS) method was developed to elucidate the impurity profiles of paclitaxel and paclitaxel injections from different Chinese pharmaceutical companies. The fragmentation patterns for paclitaxel and the related impurities were analyzed and summarized. To remove the interference from auxiliary materials, such as hydrogenated castor oil, paclitaxel was dissolved in ethanol for acid, base, peroxide, and light induced forced degradation analysis, which could produce all the impurities exist in the paclitaxel injection. A total of 10 impurities were characterized, such as cephalomannine (1), 7-epi-10-deacetylpaclitaxel (2), 7-epipaclitaxel (3), baccatin Ⅲ (4), ethyl ester side chain (5), 7-epi-baccatin Ⅲ (6), 10-deacetylpaclitaxel (7), paclitaxel isomer (C3-C11 bridge) (8), paclitaxel isomer (9), and N-benzoyl-(2R, 3S)-3-phenylisoserine (10), respectively. Among them, compounds 1-3 could be introduced during manufacture processing. In the forced degradation studies, while acid induced degradation products included 3-7, base induced degradation could produce 2-7 and 10; while 7 is the main compound produced by hydrogen peroxide treatment, 4 compounds (3-5 and 7) were produced by high temperature environment and 5 compounds (2-5 and 9 which is the first reported) from intensity light exposure. Furthermore, 8 was the main impurity came from intensity light exposed paclitaxel powder. The results from this study provide an important reference in processing, optimization, quality control and evaluation of paclitaxel.