In order to investigate the mechanism of serum low level of high density lipoprotein cholesterol (HDLC) under the condition of hypeririglyceridemia (HTG), we studied 93 patients with non-insulin dependent diabetes.Abstract: Methods All of patients were divided into a HTGgroup (n=24) and a anormotriglyceridemia (NTG) group (n=69). The serum lipids and the apolipoprotein levels that were concerned with HDLC were meassured in all of these patients.Results in HTG group, the level of HDLC, HDL2C and the ratio of apolipoprotein A_Ⅰ(apo A_Ⅰ)/apolipoprotein Al (apo A_Ⅱ) and HDLC/apo A_Ⅱ were all significantly decreased however ,apo A_Ⅱ was significantly increased contrasting with NTG group. The multiple regression analysis showed that all above mentioned serum lipids, apolipoprotein and its ratio had a linear regression relationship with triglyceride (TG). But there were not significant difference in the HDL3C and apo AI levels between this two group. The HDL3C and apo AI had not also a linear regression relationship with TG. Conclusions All above results indicated that in HTG, the main was that the serum HDL2C level was decreased. According to no apperently changed apo AI level and decreased HDLC/apo AI retio in HTG group. When we estimated the HTG, the numbers of the high density lipoprotein (HDL) particles didn't reduce, but the combination of the apolipoprotein with the cholesterol may be influenced. In addition, according to the significant increase of apo A_Ⅱ and the significant decrease of apo AI/apo A_Ⅱ in HTG, we a also estimated that the estirizing speed of cholesterol in HDL maybe slow in HTG. Both of above mentioned reasons may lead to the serum HDL2 C level decreasing, therefore, presented a serum low level of HDLC in patients.