Although the disadvantages of trans fatty acids (TFAs) are widely mentioned, limited data are available on the TFAs contents of Iranian foods, including fast foods. The aim of this study was to quantify the amounts of common fatty acids in several fast foods in Iran, with specific focus on TFAs. The most commonly consumed fast foods in Iran: sausage, calbas, hamburgers and pizzas, were randomly selected seven times from products available in supermarkets and restaurants. Each time a 10 g sample was drawn and prepared for fatty acid analysis. Total and individual fatty acids were quantified according to standard methods by gas chromatography with 60 meter capillary column and flame ionization detector. The most common saturated fatty acids in Iranian fast foods is stearic acid (C18:0) which ranged from 14.0% to 20.9%. Saturated fatty acid content in calbas was significantly higher than that found in other groups. Trans fatty acids constitute almost 23.6% to 30.6% of total fatty acids of these products. The most common TFA in these fast foods was elaidic acid (C18:1 9t). Total cis unsaturated fatty acid content of tested fast foods varied from 25.3%(in sausage) to 46.8(in calbas) with oleic acid (C18:1 9c) followed by linoleic acid (C18:2) being the most common fatty acids in these products. This study showed higher TFAs contents in commercially available fast foods compared to the amounts recommended by dietary guidelines in Iran. Further studies must assess the effects of these fatty acids on human health.