Oil is a primary metabolite and one of the three macronutrients, along with protein and carbohydrates that provide energy for our body. Oil is essential to our health because it supports a number of our body's functions. The determination of fatty acids composition was of great importance in establishing the oil quality. The qualitative and quantitative determinations of the constituents were done by gas chromatography coupled with FID detector. A total of 50 cooking oil samples of five local brands were collected from different market of Dhaka city and analyzed for relative percentage of fatty acids composition. The mean value of the relative percentage of fatty acids composition in different branded cooking oil sample were found in a range caprice (0.86-2.29%), lauric(7.01%), myristic(1.04%), palmotelic(3.19%), palmitic(32.92-76.64%), linoleic(1.55-49.82%), oleic(0.86-2.29%), stearic(2.39-8.93%), arachidic(1.20-12.14%), bhenic(0.86-2.29%) and lignoceric acid(0.86-2.29%).