Abstract: A fast and sensitive UPLC-MS/MS method was established for the direct quantification of insulin aspart in human plasma. The plasma samples were extracted by solid phase extraction (SPE), an ESI ion source was used and operated in the positive ion mode with multiple reaction monitoring (MRM). Bovine insulin was chosen as internal standard and the chromatographic separation of insulin aspart was performed on Waters ACQUITY UPLC CSH C18 column (50 mm×2.1 mm, 1.7 μm). A mixture of acetic acid aqueous solution and acetonitrile with acetic acid at a flow rate of 0.6 mL·min^-1 in gradient elution mode was employed as mobile phase. We found that the method was validated over the range of 0.200-10.0 ng·mL^-1 for insulin aspart and showed excellent linearity. The intra-and inter-assay accuracy and precision were below 14.5% and the recovery was 36.7%-41.7% over the three concentration levels evaluated. The UPLC-MS/MS method was selective, accurate, sensitive and robust, and the method was successfully applied in supporting the pharmacokinetic research of two insulin aspart injections (Test Product and NovoRapid^®) in heathy male subjects. This clinical trial was approved according to the Ethics Committee of West China Hospital, Sichuan University (2017 Clinical Trial (Western Medicine) Approval (148)).