Objective To evaluate the association between small,dense low-density lipoprotein cholesterol (sdLDL-C)and severity of coronary atherosclerosis disease (CAD).Methods A total of 436 outpatients with suspected coronary atherosclerotic heart disease (CAD) and underwent coronary computed tomography (CT) were consecutively enrolled from July 2015 to March 2016 in Fuwai Hospital.Correlations between serum sdLDL-C and the severity of CAD including characteristics of plaque,the number of stenosed coronary vessels,the degree of stenosis were analyzed.Results sdLDL-C was positively correlated with apolipoprotein B (apoB),triglyceride (TG),total cholesterol (TC),low-density lipoprotein cholesterol (LDL-C),blood glucose (Glu)with the coefficient correlation 0.644,0.631,0.558,0.434 and 0.145 successively(P ＜ 0.01),and negatively correlated with high-density lipoprotein cholesterol (HDL-C) (r =-0.241,P ＜ 0.01).sdLDL-C and apoB were the risk factors for severe CAD (triple-vessel disease and severe stenosis),independent of traditional risk factors (age,gender,hypertension,diabetes,smoking,alcohol consumption)and the use of lipidlowering agents.For the patients with triple-vessel disease,odds ratio of LDL-C,sdLDL-C and apoB were 1.936,2.673 and 31.707 respectively.For the patients with severe stenosis,LDL-C was not an independent factor,while sdLDL-C and apoB still had predictive value (odds ratio were 2.000 and 9.457 respectively).Conclusion sdLDL-C should be a predictor of severe CAD independent of traditional risk factors that may be useful for further risk stratification in the patients with CAD.