Aim To investigate the correlations between carotid plaque types, non-HDLC/HDLC and non-HDLC in patients with acute coronary syndrome (ACS). Methods This study consists of 95 patients with ACS, 30 patients with stable angina pectoris (SAP), and 49 healthy individuals who have no history of heart diseases serving as controls. All the selected cases underwent ultrasound examination of their carotid artery to diagnose carotid plaque types. The carotid plaques were classified into three types:soft plaque, fibrous plaque and calcified plaque. Their serum total cholesterol (TC), high density lipoprotein cholesterol (HDLC), triglyceride (TG), and low density lipoprotein cholesterol (LDLC) levels were measured and recorded, and the non-HDLC/HDLC ratio was calculated. Results The results showed that, non-HDLC/HDLC ratio was higher in ACS patients (P＜0.05 or P＜0.01) as compared to the SAP patients and the control subjects. The HDLC level was observed to be lower in ACS patients compared with the controls (P＜0.05). An increased level of non-HDLC was seen in ACS patients compared to the SAP patients (P＜0.05).The prevalence of carotid plaque within the ACS patients was significantly higher than that of the control subjects (P＜0.001). The prevalence of soft plaque was significantly higher (P＜0.05) and the prevalence of fibrous plaque was significantly lower (P＜0.05 or P＜0.01) in ACS patients than in SAP patients and control subjects. It was observed that the level of non-HDLC and non-HDLC/HDLC ratio were high in all the three types of carotid plaque, but the non-HDLC (P＜0.01) level and non-HDLC/HDLC ratio (P＜0.05) in the soft plaque group was significantly higher than in calcified plaque group. The receiver operating characteristics (ROC) curve analysis was used to calculate the area under the curve (AUC) for non-HDLC and non-HDLC/HDLC in ACS patients with soft plaque, which showed that AUC of non-HDLC was 0.722±0.060 (95%CI was 0.604～0.841, P＜0.01) and AUC of non-HDLC/HDLC was 0.669±0.062 (95%CI was 0.548～0.790, P＜0.01), respectively. Conclusion Our findings support that the higher level of non-HDLC/HDLC ratio is a risk factor for soft plaque in patients with ACS. Non-HDLC and non-HDLC/HDLC ratio can be considered as predictors for soft plaque in patients with ACS.