Abstract: OBJECTIVE To investigate pharmacokinetic and bioequivalence of tacrolimus sustained release capsule in beagle dogs. METHODS Six beagle dogs were randomly divided into 2 groups. A single oral dose of 3 mg of test or reference capsules were delivered to each dog in an open crossover test. The blood concentration of tacrolimus was determined by LC-MS/MS detection, and the pharmacokinetic parameters were calculated with WinNonlin 6.3 program by a computer. Based on the parameters of pharmacokinetic and relative bioavailability, the bioequivalence of tacrolimus was evaluated. RESULTS The pharmacokinetic parametes of the test and reference preperations were as follows: T_max was (1.08±0.41)h and (0.83±0.13)h, C_max was (11.63±1.35)ng·mL^-1 and (14.83±4.70)ng·mL^-1, AUC_0-48 was (62.93±32.06)h·ng·mL^-1 and (62.89±28.14)h·ng·mL^-1, t_1/2 was (10.90±4.26)h and (10.99±3.12)h in 2 groups respectively. After taking oral test capsule, beagle dog shows no noticeable T_max，t_1/2 variation between test and reference capsule; The C_max is about 85.34% of the reference capsule that is located within the 90% confidence interval of 87.21%-102.16%; The relative bioequivalence (AUC_last，test/AUC_{last，reference}) is 99.42%, that is with in the 90% confidence interval of 85.53%-115.56%, it shows that the test and reference capsule is close in effects. CONCLUSION The test and reference preparation of tacrolimus are bioequivalent.