Spermatogenesis required lots of genes taking part in this process. In prevision studies, Odf1, Odf2, Sak57, Spag4, Spag5 were identified in mouse and rat sperm tail developing. Two ESTs, BG101130 and BG100990, which coded amino acid sequences with high homology to rat Spag4, were found from mouse spermatocytes. By electrical hybridization, a 1 155 bp sequence was obtained and named as SRG4 (Spermatogenesis Related Gene 4) (GenBank accession number: AY307077), which included the full-length sequence of mouse testis hypothetical gene AK006225. The opening reading frame of SRG4 was 87 approximately 1 133 bp, and was proved by RT-PCR in mouse testis. The information analysis showed SRG4 gene was located in 2H1-H2, and the putative protein was 348-amino acid with a coiled-coil region, suggesting SRG4 might function as a transmembrane protein. The homologies of amino acid sequences were 74% between TSARG4 and SRG4 gene and 45% between SRG4 and rat Spag4 gene, respectively. RT-PCR and Northern blot results showed SRG4 gene expressed specifically in mouse testis. Changes of SRG4 expression in mouse different developing stages were observed. The results showed SRG4 gene expressed slightly in two weeks postpartum, and expressed abundantly from three weeks, and reached the top at 4 -5 weeks. This indicted SRG4 gene may play an important role in mouse spermatogenesis.