Aims: There has been no evidence on the effects of evolocumab, protein convertase subtilisin/kexin type 9 (PCSK9) inhibitor, on small size LDL. We observationally investigated the efficacy and side effects of evolocumab on the LDL subfraction particle diameter using PAGE system for lipoprotein analysis. Methods: We defined 30 patients with high-risk hyperlipidemia. As for analysis of LDL subfraction profile, we used polyacrylamide gel electrophoresis three methods: 1) 3% nondenatured poly-acrylamide gel electrophoresis method (3%PAGE), 2) 2% -16% nondenatured poly-acrylamide gradient gel electrophoresis method (2% -16% GGE) and 3) 2.7% -5% GGE. Evolocumab 140 mg/day administered together with statin significantly improved serum total cholesterol (TC), triglyceride (TG), high-dense lipoprotein-cholesterol (HDL-C), and LDL-C after four-week treatment. Results: TC, TG, HDL-C and LDL-C levels were improved by, respectively, 33%, 20%, 10%, and 54%. The mean LDL size significantly increased from 25.6 ± 0.4 nm to 26.4 ± 0.8 nm. The small dense LDL-cholesterol (sdLDL-C), large buoyant LDL-cholesterol (lbLDL-C), and mid-band lipoprotein-cholesterol were reduced, respectively. Therefore, the preliminary study on this paper can be the first step into a new insight on the world of lipid metabolism. Conclusion: Short-term adminisHow to cite this paper: