Objective: We aimed to investigate the relationship between ABO blood groups and complexity of coronary lesions assessed by SYNTAX score (SS) in stable coronary artery disease (CAD) patients. Methods: Our cross-sectional and observational study population consisted of 559 stable CAD patients. From all patients, ABO blood group was determined and the SS was calculated as low SYNTAX score (0-22), intermediate SYNTAX (23-32) score and high SYNTAX score (>32). Statistical analysis was performed using Student's t-test or Mann-Whitney U test, ANOVA, or Kruskal-Wallis test and chi-square test. Multiple logistic regression analysis was used to identify the independent predictors of high SS. Results: The analysis between the SS tertiles revealed that the frequency of non-O blood group was significantly higher in the upper SS tertiles (56.2% vs. 75.9 vs. 80.2%, p<0.05). However, the frequencies of Rh types were similar in all tertiles. Multiple logistic regression analysis was applied for determining the predictors of high SS. Accordingly, non-O blood group (OR: 2.68, 95% CI 1.65-4.35, p<0.001), LV-EF (OR: 0.93, 95% CI 0.91-0.95, p<0.001), LDL(OR: 0.98, p<0.001), and e-GFR (OR: 0.99, 95% CI 0.98-0.98, p<0.001) were found to be the independent predictors of high SS. Conclusion: We showed that there were significant associations between ABO blood groups and complexity of angiographic CAD.