OBJECTIVE This study investigated the effects of conjugated linoleic acid (CLA) on the body weight, fat deposition and the expression of stearoyl coenzyme A desaturase 1 (SCD1) in the livers of male ICR mice that were fed with either beef tallow (BT) or fish oil (FO) supplemented with CLA. Mice weighing 25-30 g were divided into four groups, BT and BT supplemented with 0.5% CLA (BTC), FO and FO supplemented with 0.5% CLA (FOC). Each group consisted of 8 mice, and they were fed the experimental diets for 4 weeks. The experimental diets were composed of 59.18% carbohydrates, 19.73% proteins and 21.09% fat in terms of their contributions to total calories, and other nutrients were identical. CLA was added to the diets of the CLA supplementation groups at 0.5% (w/w). The measurement of triglyceride (TG) was done by using a kit. Fatty acid compositions were analyzed in both the plasma and the liver using a gas chromatograph. The levels of SCD1 expression were analyzed by RT-PCR in the liver. RESULTS No significant difference was found in the levels of food intake, body weight and food efficiency among experimental groups. However, the levels of both epididymal and visceral fat weight were significantly lower in the CLA-supplemented groups, BTC and FOC (p < 0.05). The level of the triglyceride concentration was also significantly lower in the CLA-supplemented groups (p < 0.05). The levels of the liver SCD1 gene expression were also higher in the CLA-supplemented groups. However, significant inhibition of conversion from C16:0 to C16:1 was found in both fatty acid compositions of the liver (p < 0.05). CONCLUSIONS Addition of 0.5% CLA did not inhibit the liver SCD1 gene expression; however, it showed decreasing effects on the fat pad weight, the concentration of TG and on fatty acid composition, leading to a decrease in the fat depositions. Such effects were clearer when CLA was supplemented to BT rather than FO.