Background: Dietary lipids may lead to significant changes in the composition of cell membrane structure. Objective: The association between red blood cell (RBC) membrane fatty acid composition and dietary fatty acids intake in obese adolescents with and without metabolic syndrome was investigated. Methods: Ninety-six adolescents (59 obese and 37 lean) were included in the study. The obese subjects were divided into two groups with (n=26, aged 12.3 years) and without (n=33, aged 12.7 years) metabolic syndrome. The mean age of lean participants was 11.8. The criteria for metabolic syndrome were: 10 <16 age group; BMI >= 95th percentile, triglycerides >= 150 mg/dL, HDL- C< 40 mg/dL, blood pressure systolic >= 130, diastolic >= 85 mm Hg, glucose >= 100 mg/dL. Subjects with any 3 of these 6 items were accepted with metabolic syndrome. Nutrient intakes were recorded for 3 days by a dietitian. Anthropometric and blood chemistry variables and RBC membrane fatty acid levels were measured. Results: BMI, BMI-SDS, body fat percentage, blood pressure, TG, ALT, insulin, HOMA-IR levels (p<0.001) of obese were significantly higher than lean adolescents whereas HDL-C levels were lower (p<0.001) in obese than lean. Fiber, C22:1 omega-9 MUFA, C20:4 omega-6 PUFA consumption were higher (p<0.05) in obese with metabolic syndrome. Consumption of total omega-3 PUFAs were higher (p<0.05) in obese with metabolic syndrome and in leans than those without the metabolic syndrome. The RBC membrane C16:1 omega-7 fatty acid levels were higher but C20:5 omega-3 levels were lower (p<0.001) in obese. Diet fiber was positively associated with RBC C16:1 omega-7 fatty acid (r=0.239, p<0.05). A positive slight correlation was determined between diet and RBC membrane C20:5 omega-3 (r= 0.200, p= 0.051). Conclusion: Dietary fatty acids affected some anthropomenic measurements and blood chemistry. The RBC membrane C20:5 omega-3 slightly correlated with diet C20:5 omega-3.