To study the bioequivalence of a kind of progesterone sustained release suppository, a randomized cross-over study was conducted in 12 rabbits. A single rectal dose of 2.75 mg/kg progesterone sustained released suppository (tested formulation, T) and progesterone suppository(reference formulation, R) was administered; a multiple dose of 2.75 mg/kg was given up to seven times with an interval of 8 h. Concentrations in serum were determined by a competitive enzyme immunoassay. The main parameters of T were: for single and multiple doses, Cmax was 48.8±11.8ng/mL and 43.5±9.4 ng/mL, Tmax was 0.5±0.3 h and 0.4±0.3 h, AUC(0-24h) was 362.4±143 ng·h·mL-1 and 310.6±70.3ng ·h·mL-1,respectively.The relative bioavailability of T to R were ( 104.2 ±13.4) % and ( 111.4 ± 19. 1 ) %, respectively. Statistical analysis showed that the two formulations were bioequivalent and T had sustained released feature.