The purpose of this study was to evaluate the effects of pulsed ultrasound on wound healing and observe during the wound healing process the distribution of mast cells according to histopathologic findings. Eighty Sprague Dawley rats which were divided into 4 groups received full thickness skin wounds on the back. Each of the 5 animals was sacrificed immediately and then sacrificed again 1, 3, 6, and 12 days after injury. Specimens from the wounds were removed during healing and routinely processed with a hematoxylin-eosin stain and a toluidine blue stain. The authors then observed the distribution of mast cells under a light microscope. The results of this study were as follows: The rate of wound healing and the length of the wounds of the pulsed ultrasound group II was significantly faster than group I on day 6 and day 12 (p<.001). Group III showed the most significant effect after12 days (p<.001). Group IV also showed a significant effect at 12 days (p<.01). A low-intensity ultrasound .5 $W/cm^2$ resulted in a fast healing rate. During the wound healing process mast cells had a tendency to decrease in the acute inflammatory phase. During the wound healing process mast cells were thought to contribute to the healing of the wound.