An recombinant vector pCSV-EPO for expression of EPO cDNA in mammalian cells was constructed by the techniques of gene recombinant, PCR amplification and region-specific mutagenesis. The pCSV-EPO was introduced into COS7 cells by DEAE-dextran-mediated transfection. The expression of the EPO was demonstrated by EPO-ELISA assay. At 48h post transfection, the EPO level was 25ng/ml and 72 h was 17ng/ml.