Electrical stimulation therapy (EST) of lower esophageal sphincters (LES) is a new technique for the treatment of gastroesophageal reflux disease (GERD). In this paper, an implantable LES stimulator with wireless power transmission is proposed for the treatment of GERD. The LES stimulator is composed of an implantable pulse generator (IPG), an external controller, and a wireless power transmission module. The IPG, whose area is 31×21 mm2, is designed to generate voltage-regulated constant-current stimulation pulses. The external controller allows for wireless programming of the IPG via a Bluetooth Low Energy (BLE) module. The wireless power transmission module provides power for the IPG. According to the measurement of output stimulus waveforms, the proposed LES stimulator is capable of delivering electrical stimulations with a current ranging between 0 and 8 mA. To evaluate the safety and efficacy of the proposed LES stimulator, experiments were performed on 12 male New Zealand white rabbits. Esophageal manometry was performed before and after the procedure and the LES pressure (LESP) has been recorded. The mean LESP is increased significantly in the stimulation group than the sham group (stimulation group: 9.25±1.24 mmHg vs 13.99 ±1.28 mmHg, p<;0.05; sham group: 9.00±1.22 mmHg vs 9.23±1.27 mmHg, p=0.267). The results show that the electrical stimulation delivered by the LES stimulator can safely and effectively increase resting LES pressure in acute animal models, suggesting that the implantable LES stimulator is a perspective approach for treating GERD in clinics.