This study was performed to observe the gross reactions of surrounding maxillary sutures to the widening of rnidpalatal suture in the dog. Three, healthy dog were chosen for the experiment. One animal was used as control, and two were used as experimental animals. . Midpalatal suture was expanded total 7mm with screw for 10 days. The following results were obtained : 1. Midpalatal suture was expanded with the most width, in which anterior was be more expanded than the posterior, and shape was wedge form. 2. Interincisive suture was definitely expanded. 3. Internasal suture and interfrontal suture were slightly expanded. 4. Expansion of frontomaxillary suture, frontoparietal suture, frontonasal suture, zygomatico temporal suture, zygomatico frontal suture, zygomatico maxillary suture, occipito mastoid suture, occipito parietal suture, naso incisive suture, naso maxillary suture, and incisive maxillary suture were not observed.