The expressed sequence tags (ESTs) of normal mouse testis were obtained from online EST database ZooDDD. Their highly homologous EST sequences were found through the dbEST database to construct contigs, and spliced by the biomedical software Biolign. The corresponding exons and introns within genome sequences were predicted by software GeneScan. According to the open reading frame, the primers were designed. RT-PCR was applied in the cloning of novel gene from mouse testis and analyzing its expression pattern in various mouse tissues. The bioinformatics analysis on the sequencing results of TSEG-1 was conducted. Results indicated that a novel gene TSEG-1 was cloned from 1 668-2 011 kb of mouse X chromosome, with full-length sequence of 510 bp. The open reading frame (ORF) is 336 bp in length and en-codes a deduced amino acid sequence of 111 residues. The molecular weight of TSEG-1 protein is 12.84258 kDa, and its pI is 11.4000. RT-PCR demonstrated the correctness of its ORF. TSEG-1 was distinctively expressed in testis, but not in other tissues of mouse. No obvious homology with other mouse cDNA was found for TSEG-1. The GenBank accession number EU079024 was achieved. It was predicted that TSEG-1 is a kind of transmembrane protein, and the transmembrane domain is from 41 amino acid residue to 61 amino acid residue. Blastn analysis revealed its high homology to human testis-specific gene H2AX. Computational prediction of the 5'-untranslated region of TSEG-1 gene revealed a 680 bp-length promoter region. There are four antigen binding sites and two phosphorylation sites of specific protein kinase in TSEG-1 protein, with subcellular localization in mitochondria. The cloning of mouse testis specific gene TSEG-1 laid a foundation for subsequent research of its biological function and expression regulation.