Background: We used virtual histology-intravascular ultrasound (VH-IVUS) to evaluate the relation between microalbuminuria and plaque components in 920 patients. Methods: Patients with albumin levels <30 mg/g of creatinine were defined as having normoalbuminuria (n=824), those with albumin levels of 30 to 300 mg/g as having microalbuminuria (n=96). Results: Microalbuminuria group was presented with more acute coronary syndrome (ACS) (72% vs. 61%, p=0.018) and was more diabetics (53% vs. 26%, p<0.001). In ACS patients, %necrotic core (NC) volume was significantly greater in microalbuminuria group compared with normoalbuminuria group (19±10% vs. 15±9%, p=0.019), but not in patients with stable angina. In ACS patients, thin-cap fibroatheroma (TCFA) was observed more frequently in microalbumiuria group (36% vs. 18%, p=0.008), and microalbuminuria was the independent predictor of TCFA (Odds ratio=1.106; 95% CI 1.025-1.144, p=0.018). In diabetic patients, %NC volume was significantly greater in microalbuminuria group compared with normoalbuminuria group (20±9% vs. 16±10%, p=0.017), but not in non-diabetic patients. In diabetic patients, TCFA was observed more frequently in microalbumiuria group (38% vs. 17%, p=0.002) and microalbuminuria was the independent predictor of TCFA (Odds ratio=1.120; 95% CI 1.038-1.204, p=0.012). Conclusions: Microalbuminuria was associated with more vulnerable plaque components in ACS and diabetic patients. More intensive medical therapy is needed to stabilize the vulnerable plaque if microabluminuria is observed in diabetic ACS patients.