AIM: To investigate the intestine and body development of intrauterine growth retardation (IUGR) rats under early different protein diet and to analyze the correlation between leptin and intestine and body development.METHODS: An IUGR rat model was established by food restriction of pregnant female rats. Fifty-six neonatal IUGR rats and 24 neonatal normal rats were randomly divided into normal control group (C group), IUGR model group (SC group), low protein diet IUGR group (SL group), and high protein diet IUGR group (SH group). Eight rats were killed per group at wk 0, 4, and 12. Serum leptin, body weight (BW), body length (BL), intestinal weight (IW),intestinal length (IL), and intestinal disaccharidase (including lactase, maltase, and saccharase) were detected.RESULTS: BW (4.50±0.41 g), BL (5.96±0.40 cm), IW (0.05±0.01 g), and IL (15.9±2.8 cm) in neonatal IUGR rats were much lower than those in C group (6.01±0.55 g,6.26±0.44 cm, 0.10±0.02 g, 21.8±2.7 cm, P＜0.05), while intestinal lactase and maltase activities were higher than those in C group. SH group showed the fastest catch up growth and their BW, BL, IW, and IL reached the C group level at wk 4. SC group showed relatively slower catch up growth than SH group, and their BW, BL, IW did not reach the C group level at wk 4. SL group did not show intestine and body catch up growth. Intestinal maltase [344±33 μmol/(min.g)] and saccharase activities [138±32μmol/(min.g)] in SL group were both markedly lower than those in C group [751±102, 258±27 μmol/(min.g), P＜0.05].There were no significant differences in lactase activities at wk 4 and disaccharidase activities at wk 12 among all groups (P＞0.05). The leptin level in SL group (0.58±0.12ng/mL) was the highest in all groups, and much lower in SH group (0.21±0.03 ng/mL) than that in any other IUGR groups at wk 4 (P＜0.05). Leptin was negatively related to BW (r= -0.556, P = 0.001), IW (r= -0.692, P= 0.001)and IL (r = -0.738, P = 0.000) at wk 4, while no correlation was found at wk 12.CONCLUSION: High protein diet is a reasonable early nutritional mode to IUGR rats in promoting intestine and body catch up growth.