To study the possibility of attraction magnetic forces to expand maxillary arch, we used 2 big adult dogs, 2 small puppies, 1 small adult dog as experiments, and 1 small adult dog as a control. We measured the intercanine width and intermolar width and histologically observed in the suture and cervical and apex region of teeth and took occlusal X-rays to observe separation of suture line in the maxilla. The results were as follows: 1. Expansion velocities of intercanine (0.25mm/day) and intermolar widths (0.23mm/day) in puppies were faster than those (0.135mm/day, 0.09mm/day) in adults. 2. In all experiments in adults (0.135mm/day) and puppies (0.25mm/day), expansion velocity of intercanine widths were faster than those (0.09mm/day, 0.23mm/day) of intermolar width. 3. In all experiments ectatic changes were observed and cellularities of fibroblast increased in the suture line. Only in adults dogs the separations of palatal suture were observed in the occlusal X-ray view. 4. In the puppies bony deposition was particularly observed in the suture line and micro-bony fragments were often observed. 5. In the all experiments no root resorption was observed in the cervical and root area, but normal root resorption due to eruption of permanent teeth was observed in the puppies.