The present study was conducted to show that dietary supplementation with a fungus, Aspergillus awamori, modifies muscle fatty acid profiles in broiler chickens. A total of thirty chicks, selected from a group of 100 chicks aged 15 d, were divided into a control group and two treatment groups (ten birds per treatment). The control group was fed a basal diet, and the treatment groups were fed basal diets supplemented with A. awamori at levels of 0·05 and 0·2 %. From the start of the study at 15 d, the birds were raised for an additional 12 d, and growth and the muscle fatty acid profile were evaluated. Although feed intake was decreased by the fungus, body-weight gain and breast muscle weight were increased, and thus, feed efficiency was improved. Abdominal fat and plasma cholesterol and TAG were decreased, while plasma HDL-cholesterol and breast muscle fat content were increased. Interestingly, muscle α-tocopherol content was increased and muscle thiobarbituric acid-reactive substances were decreased by A. awamori. Furthermore, there was an observed decrease in SFA and an increase in unsaturated fatty acids in the muscle fat due to the fungus feeding. The mRNA of fatty acid synthase, acetyl-CoA carboxylase and Δ-6 desaturase in the muscle were all increased, while the mRNA of 3-hydroxyl-3-methylglutaryl-CoA reductase and carnitine palmitoyl transferase 1A were decreased by the fungus. In conclusion, the present study clearly shows that the muscle lipid profile could be modified by the addition of A. awamori to the diet.