A new formulation tablet B was developed and compared with tablet A with the purpose of improving the bioavailability of benorilate by reducing its particle size. The dissolution rate in vitro was determined by paddle method and using surfactant solution medium. The plasma concentrations of hydrolyzates which are salicylic acid and paracetamol from benorilate in vivo were measured by HPLC. The dissolution rates of ground and unground drug are 0.0337 min-1 and 0.0152 min-1 (P < 0.001) respectively. Compared with tablet A, the cumulative dissolution percentage of B is higher. The mean dissolution time of B and A are 15.77 min and 42.25 min (P < 0.001) respectively. The study in vivo showed that the Cmax, Tp and AUC of salicylic acid for these two formulations have no significant difference (P > 0.1). The relative bioavailability of B to A is 125.59%. Their in vivo process fits one-compartment model and first order elimination.