Introduction: A suitable LC-MS method for the quantitative determination of genotoxic impurities such as alkyl p-toluene sulfonates in Cabazitaxel was developed. Alkyl p-toluene sulfonates were estimated by LC-MS method using Waters Symmetry C18 (75×4.6 mm), 3.5 µ column. Materials and Methods: Column temperature was maintained 40 °C. Injection volume was 10 µL and flow rate was set as 0.8 mL/min. Sampler temperature was maintained to 25 °C and run time was set as 25 minutes. The mobile phase was a mixture of ammonium acetate buffer and acetonitrile in 70:30(v/v) was used. Results: The method validation has been carried as per ICH guidelines. LOQ was found to be 2.66 µg/mL, 2.75 µg/mL and 2.55 µg/mL for MPTS, EPTS and IPPTS Alkyl p-Toluene Sulfonates (APTS) respectively. Conclusion: The proposed Liquid chromatography-Mass spectroscopy method that can quantify genotoxic APTS in Cabazitaxel at low-level concentration has been developed and validated as per ICH guidelines. Hence, the proposed method was recommended for the assay of genotoxic impurities of cabazitaxel in dosage forms in busy pharmaceutical laboratories.