【Objective】The pharmacokinetics and bioavailability of the triamilide antimicrobial, tulathromycin, were investigated in swine. 【Method】Thirty pigs received 2.5 mg?kg-1 of tulathromycin injection by either intravenous (i.v.) or intramuscular (i.m.) route in three studies: study A (0 pigs, i.v.) ,study B (0 pigs, i.m, Huizhong, China.) and study C (0 pigs, i.m, Pfizer,USA.). Blood samples were collected and analysed by high-performance liquid chromatography (HPLC) with tandem mass pectrometry detection (LC-MS/MS) using ESI. Pharmacokinetic parameters were estimated using the WinNonlinTM software package and SPSS 16.0 analysis of the time and concentration data. 【Result】The tulathromycin concentration time data were fitted to noncompartment model. After i.v. injection plasma clearance (Cl) was 182.7 mL?h-1?kg-1, the volume of distribution at steady-state (Vss) was 17.2 L?kg-1 and the elimination t1/2 was 64.8 h. Statistical analysis on plasma showed that there were no signi?cant differences between pharmacokinetic parameters (P＞0.05).Compared with tulathromycin (Pfizer,USA.), the relative bioavailability (Huizhong, China) following i.m. administration was 117%,the absolute bioavailability (Huizhong, China) following i.v. administration was 112%. It appeared that tulathromycin was rapidly absorbed , eliminated slowly and highly bioavailable . 【Conclusion】The results indicate that the two formulations are bioequivalent in both the rate and extent of absorption.