This study evaluated the effect of the dietary replacement of sunflower oil with perilla oil in Nile tilapia (GIFT strain) at 0, 10, 20 and 30 days. There was an increase in total omega 3 fatty acids (n-3) in muscle tissue (from 63.6 to 181.5 mg g(-1)) and a decrease in total concentration of omega 6 fatty acids (n-6) ranging between 255.6 and 196.1 mgg(-1). Amongst the n-3 fatty acids, the concentrations of alpha-linolenic acid (18:3n-3) and docosahexaenoic acid (20:6n-3) increased by 9.4 and 1.9 times, respectively, after 30 days for the perilla oil-enriched diet. The n-6/n-3, polyunsaturated and saturated fatty acids (PUFA/SFA), and polyunsaturated and monounsaturated fatty acids (PUFA/MUFA) ratios tended to stabilize after 20 days under the perilla oil-enriched diet. Incorporation of perilla oil as a lipid source in the diet of tilapia for 20 or 30 days resulted in significant changes in the fatty acid composition of the fish muscle tissue, contributing to increase its nutritional value.