Eight healthy male adult guinea pigs were divided into four groups. Skin incisions were made on each Side of the back of each with CO_2 laser and scalpel respectively, and were sutured. Post-operative samples were taken on the 3rd, 5th, 7th and 14th days, and histological preparations were studied. The results were as follows:1. The healing process of CO_2 laser incisions were obviously retarded in comparison with those of scalpel, and usually produced a bigger scar.2. Laser caused the tisues of the cutting edges to coagulate, thus produced a sort of haemostasis.3. In laser incisions there were almost five times as many of mast cells being observed during the healing process than those by scalpel. It needs further studies to make sure whether it is related to the repair and defence of organism.4. Gleaned up the burnt tissues with 0.1％ Benzalkonium bromide seemed to have the effect of preventing infection and accelerating the healing process.