Background: n-3 fatty acids and lifestyle are closely related to risk of myocardial infarction (MI). However, little is known about recommended value of omega-3 index in patients with acute MI taking statin treatment. The purpose of this study was to test the hypothesis that lower omega-3 fatty acids and/or smoking are associated with the risk of the MI, even taking statin treatment. Methods: Twenty-four cases with MI taking statins, confirmed by coronary angiography, and sixty-eight controls without MI were recruited for the study. The omega-3 index was calculated as the sum of EPA and DHA in erythrocyte (RBC) membranes. Lifestyle factors and dietary intakes were assessed using a questionnaire. Multivariate adjusted regression analysis was used to assess independent associations between acute MI, omega-3 index, and lifestyle factors. Results: The omega-3 Index was significantly lower in cases (8.83%) than controls (11.13%; P<0.001), however total trans-fatty acids were not differ between groups. Fish intake in acute MI was more frequent than control. The omega-3 Index was associated with decreased risk of acute MI (OR 0.16 (95% CI 0.03-1.14); P=0.047), while smoking were associated with an increased risk of acute MI (OR 6.67 (95 % CI 1.77-25.23) after the adjustment for age, gender, body mass index, alcohol drinking. Smoking wasn't related to the omega-3 Index. Conclusion: Smoking and lower omega-3 index are associated increased risks of acute MI, even they were given statins. An omega-3 index of at least 11% and abstinence seem to be associated with the greatest cardioprotection for Korean.