Abstract: Because many tumor cells secrete potent stimulants of endothelial cell growth,we successfullycloned bovine pulmonary artery endothelial cells by limiting dilution in a mixture of normal culture mediumand human lung A₅₄₉ cell line postculture medium（1:1）.The purity of cloned endothelial cells were 100%after long culture,while the ability of endothelial cells secreting nitric oxide and endothelial cells proliferationdidn’t alter significantly.