Alternative splicing of exon 6 in Fas pre-mRNA generates a membrane bound pro-apoptotic isoform or soluble anti-apoptotic isoform. SRSF4 is a member of Arginine-Serine rich (SR) protein family. Here we demonstrate that increased SRSF4 expression stimulates exon 6 inclusion, and that reduced SRSF4 expression promotes exon 6 exclusion. We also show that weaker but not stronger 5' splice-site strength of exon 6 abolishes the SRSF4 effects on exon 6 splicing. Furthermore, we identified a novel enhancer on exon 6, on which SRSF4 interacts functionally and physically. Our results illustrate a novel regulatory mechanism of Fas pre-mRNA splicing.