Abstract：Objective：To optimize specific precipitation method for separating low density lipoprotein (LDL) from human plasma, and develop a new method to characterize the LDL particle size. Methods：LDL was rapidly precipitated from human plasma by using heparin citrate buffer. The size of LDL particles was determined by Zeta potential with high resolution and nanoparticle size analyzer. The morphologic appearance of the particle was observed by transmission electron microscopy. The size and shape of the particle were compared with those separated by ultracentrifugation. Results：The purity of LDL separated by either precipitation or ultracentrifugation method achieved electrophoresis level since the electrophoresis showed only one band of LDL The sizes of LDL separated by heparin citrate buffer precipitation and ultracentrifugation were (31.7±1.1) and (32.9±0.8) nm respectively and no statistical difference was found. The roundish shapes of LDL particle separated by both methods were similar. Conclusion：Compared with the ultracentrifugation, heparin citrate buffer precipitation method was easily and rapid for separating LDL with high purity. The determination for LDL particle size by Zeta potential with high resolution and nanoparticle size analyzer was simple and cost-saving.