Aim To study the relation between cholesterol ester transfer protein (CETP) gene mutation and size of low density lipoprotein (LDL) particle. Methods Exon 15 missense mutation (442D∶G) in CETP was determined using PCR-RFLP method in 200 patients with coronary artery disease (CHD). LDL particle size was analyzed by non-denaturing polyacrylamide gradient gels. Results 6 heterozygotes and 1 homozygote were found to had the 442D∶G mutation among 200 CHD patients. Frequency of this mutation was 3.5%. The patients with gene mutation (n=7) had significantly larger particle diameters than those without the mutation (n=40) (26.92±0.79 nm vs. 25.71±0.66 nm, respectively;P<0.01). LDL subfraction pattern in all the patients with gene mutation is pattern A. The distribution of LDL subfraction pattern was significantly difference between two groups. The patients with gene mutation had decreased plasma CETP level, while elevated level of HDLC and apoA_Ⅰ compared with control. Conclusion LDL particle size in patients with CETP gene mutation increases.