Abstract: This paper developed a sensitive and specific liquid chromatography-electrospray ionization mass spectrometry (HPLC-MS/MS) method for the determination of decapeptide LXT-101 in Beagle dog plasma. Plasma samples spiked with internal standard (IS) were treated with acetonitrile to precipitate the protein. Selected reaction monitoring (SRM) using the precursor → product ion combinations of m/z 472.1→587.9 and m/z 502.8→633.8 were used to quantify LXT-101 and IS, respectively. The linear calibration curves were obtained in the concentration range of 0.5-500.0 ng·mL^-1. The limit of quantification (LOQ) was 0.5 ng·mL^-1. The inter-day and intra-day precision (RSD) across three validation run over the entire concentration range was below 10.9%, and the accuracy (RE) was within ±1.8%. The main pharmacokinetic parameters of LXT-101 after muscle injection of 20 μg·kg^-1 were as follows, AUC_0-t: (176.8±116.7) μg·h·L^-1, MRT_0-t: (2.52±0.53) h, T_1/2: (1.4±0.3) h; CL: (0.16±0.09) L·h^-1·kg^-1, and V_d: (0.30±0.16) L·kg^-1, respectively. The method is proved to be specific, sensitive and suitable for the investigation of LXT-101 pharmacokinetics in Beagle dog.