Two adult rhesus monkeys were chosen for the experimental study of maxillary expansion with magnetic force. The duration of experiment was 70 days. The following methods were applied: 1. measuring the width between the two canines and the width between the two first molars on the casts, 2. taking occlusal radiographs for the observation of premaxillary and midpalatal sutures. 3. observing the histological sections under the microscope. The results showed the width of 3 to 3 and the width of 6 to 6 significantly increased, associating with the adaptation of periodontal tissues to the action of magnetic force.