This study is to investigate the effect of dietary L-carnitine supplementation on lipid metabolism in rats fed with isolated soy protein and casein for their source of protein. Four experimental groups were organized and each group had eight Sprague-Dawley male rats with the initial weight of around 180g. The four groups were CO (casein only supplemented group); CC (casein and 3% L-carnitine supplemented group); ISO (isolated soy protein only supplemented group); ISC (isolated soy protein and 3% L-carnitine supplemented group). All groups were supplemented with the experimental diet for four weeks and carnitine comprised 3% of. their diet. The results were as follows; 1. There was no significant difference in food intake among the groups. 2. Final weight gain was significantly lower in the groups supplemented with isolated soy protein than in the groups supplemented with casein (P<0.05). The groups with supplemented casein and carnitine showed the effect of weight reduction (p<0.05). 3. Food efficiency ratio was lower in the groups supplemented with isolated soy protein than in the groups supplemented with casein (p<0.01). The groups supplemented with casein and carnitine showed low food efficiency ratio. 4. The serum total lipid was higher in the groups supplemented with casein than in the groups supplemented with isolated soy protein (p<0.05). 5. Serum total cholesterol was higher in the groups supplemented with casein than in the groups supplemented with isolated soy protein. 6. There was no significant difference in triglyceride, HDL-cholesterol, and LDL-cholesterol in serum among the groups. 7. Out of the groups supplemented with isolated soy protein the total cholesterol level in liver was low in the groups to which carnitine was supplemented (p< 0.05). However, there was no significant difference of liver total lipid and triglyceride among the groups. 8. There was no difference in TBARS levels and GSH-Px activities in liver among the groups.