Objects: This study aimed to explore which is an independent predictor of major adverse cardiac event in type 2 diabetic patient with acute coronary syndrome who underwent percutaneous coronary intervention (PCI). Subjects & Methods: There was a total of 122 patients (79 men and 43 women) who underwent PCI due to acute coronary syndrome (unstable angina, acute myocardial infarction) with type 2 DM. Six month follow-up coronary angiogram was performed at 6 months after PCI. The patients were divided into two groups according to major adverse cardiac events (MACE; cardiac death, reinfarction, target vessel revascularization): Group I (n=52) with MACE and Group II (n=70) without MACE. Plasma homocysteine, Hgb A1c, WBC counts, high sensitive CRP, ESR, lipid profile, glucose, fibrinogen and ejection fraction (EF, %) were estimated. Results: Baseline characteristics were not different between two groups. There was no difference in coronary angiographic findings between two groups. There was no difference in other laboratory data. The patients with higher homocystein level (higher than 12 關mol/ L) showed a significantly higher rate of MACE than those with lower homocystein level (p=0.022, OR: 2.47, 95% CI; 1.13~5.42). Plasma homocysteine at sixth months follow up was significantly elevated in Group I compared with Group II (11.7짹4.8 vs. 9.7짹3.3, p=0.045). Conclusion: The high level of plasma homocysteine was a predictor of major adverse cardiac event after PCI in diabetic patients with acute coronary syndrome.