Abstract: This experiment was conducted to study the tissue residues of tulathromycin in swine, preparing for the determination of the withdrawal time. Pigs received 2.5 mg·kg^-1 of tulathromycin by intramuscular(i. m.) route. Animals were sacrificed at 12 hours and 5, 12, 18, 25, 36, 48 days after administration. Tulathromycin was extracted from tissues by adding acetonitrile. The supernatant was defatted by adding N-hexane, then was applied to the C₁₈ SPE cartridge.The identification was carried out by LC-MS/MS. The concentration of tulathromycin in tissues was calculated by Analyst 4.1.5 software. The results indicated that injection site held the highest residue level at 12 hours, while the concentration of tulathromycin in all of the tissues at 36 days was lower than the Maximum Residue Limit(MRL).The pharmacokinetic parameters were estimated using WinNolin software package. The results showed that the elimination rate was injection site＞liver＞skin+fat＞muscle＞lung＞kidney, with the elimination half-life of 117.06, 193.14, 197.60, 207.64, 228.99, 232.61 h respectively. Compared with other tissues, the area under the plasma concentration-time curve(AUC) in lung (1 220.59 μg·h·g^-1)was greater than in muscle, liver and skin+fat, lower than injection site and kidney. Kidney was considered as the metabolically active organ, so it suggested that lung was the target organ According to the MRLs set by EU and USA, etc, the longest withdrawal period was suggested in injection site, 33days. The results demonstrated that the absorption and distribution of tulathromyxin was wide. Besides, the active time is long. It is proposed that the withdrawal time should be 33 days after administration.