The experiment was undertaken to study the effect of total parenteral nutrition (TPN) on nitrogen balance and organs in the postoperative period, 73 of six-week old rats were devided into four groups as follows. Group Ⅰ Simple laparotomy and oral feeding Group Ⅱ Simple laparotomy and TPN Group Ⅲ Intestinal bypass operation and oral feeding Group Ⅳ Intestinal bypass operation and TPN TPN groups received 338 cal/kg/day and 1,96Ng/kg/day administered continuously throughout 13 days. The body weight increase in group Ⅰ, Ⅱ, Ⅲ, and Ⅳ were 66,6g, 55,6g, 4,6g and 42,5g, respectively. The weight gain was observed in TPN groups during postoperative period. The nitrogen balance study in group Ⅱ and Ⅳ showed that positive nitrogen balance was able to achieve in both group and cumulative nitrogen balance in group Ⅱ and Ⅳ was 1,65g and 1,31g, respectively. This study shows that positive nitrogen balance can be obtained in the immediate postoperative period by means of TPN. Small intestine during TPN showed significantly lesser in weight and shorter in villous height than that of oral feeding. The lack of absorption of nutrients from intestinal mucosa seems to be responsible. Histological studies of TPN group revealed that liver and spleen had fatty infiltration and there was swelling of reticuloendothelial cells which is supposed to be due to infusion of fat emulsion. Swollen cells of tubules in the kidney were observed.