Leukemic cells from patients expressed high level FasL cause apoptosis of autologous activated T cells via the Fas/FasL pathway. To investigate the role of soluble Fas (sFas) in reversing this process, a retroviral-mediated expression vector pLXIN-sFas was established. A retroviral-mediated expression system of human sFas was established in vitro and the biological activity of the expression product sFas was observed. To obtain the soluble Fas cDNA, the specific part of the full-length Fas cDNA was deleted by multiple PCR. After pLXIN-sFas packaged by PA317 cells, it was transferred into the target cell COS-7. The quantity of the sFas was (2.2 +/- 0.7) micro g/ml in supernatant of cultured COS-7 cells, and it could greatly inhibit apoptosis of Jurket cells induced by anti-Fas antibody. Our results suggested that the recombinant is able to express the target proteins in vitro and it has the perfect biological activity.