The purpose of this study was to investigate the effects of wax gourd on body weight, body fat, triglyceride, leptin and fat cell size in rats fed medium fat Male Sprague Dawley rats were fed with experimental diet containing total dietary fat at 20% of calorie with wax gourd (WG) for 4 weeks. Forty rats were divided into 4 groups including control, 5, 10, and 15% (w/w) WG supplement The results showed that weight gain was significantly higher in 5% WG than that in control (p<0.05), but was not different among the WG supplement groups. Total fat weight was significantly decreased in both 10 and 15% WG supplement groups than that of control. The levels of triglycerides and free fatty acids in the plasma were significantly decreased, particularly in 15% WG supplement group (p<0.05). The levels of leptin was not significantly different among the experimental groups. Fat cell size was significantly decreased in WG supplement groups compared to that of control group (p<0.05). Correlation among the parameters demonstrated that weight gain correlated positively with total fat weight, the levels of leptin and triglycerides. Taken these results together, 15% WG supplement diet substantially reduces total fat weight, triglycerides and free fatty acids levels and fat cell size in the rat fed midium fat.