Summary: In order to regulate the apoptosis induced by Fas-FasL system, a soluble isoform of mouse Fas was cloned from thymocytes of immature mice with the primers designed according to the full-length Fas cDNA sequence in the GeneBank. It was directionally inserted into the intermedium vector pUC19. DNA sequencing proved that it was consistent with the expected sequence.Then it was subcloned into the eukaryotic expression vector pCA13, which was used to construct the recombinant vector pCA13-FasC. By lipofectamine (LF2000)-mediated transfection, pCA13FasC was transfected into the 293 cells. RT-PCR and Western blot indicated that the murine soluble Fas C protein was expressed in the 293 cells. Apoptosis inducing test showed that the expression of this murine Fas C could block the Fas-induced apoptosis, which confirmed the biological activity of the recombinant Fas C.