Synthesis of medoxomil prodrug of ibuprofen (IM) was described. Its stabilities at different pH environments encountered in the gastrointestinal tract and in rat plasma in vitro were tested. Results demonstrated that esterase play an important role in the activation of IM. It can pass through the stomach without degradation, and with very slow degradation in intestinal tract, which indicated that IM may be absorbed with prototype in intestinal tract. While,after absorption, IM can be hydrolized very quickly by esterase in plasma. These results indicate that IM has the characteristics of prodrug.