The growth and fertilization of germ cells require the identification and characterization of their unique genes. Because the processes that take place in male germ cells are unique; that is, they do not occur in any other tissue. The testis is a specialized male gonad with complicated gene expressions for spermatogenesis and steroidogenesis. RT-PCR analysis was performed to determine whether the candidate genes selected from the NCBI database are true genes with testis-specific expressions in mice. In total, 20 testis-specific genes were selected randomly and examined in 15 adult mouse tissue samples, including the testis. The expression profiles of the 20 selected genes in the 15 mouse tissue samples showed 3 expression categories: ubiquitously expressed genes, which were detected in all types of mouse tissues; the testis-predominant genes, which were not detected in all mouse tissue samples, were strongly expressed in the testis and weakly expressed in a few types mouse tissue; and the testis-specific genes, which were exclusively expressed in the mouse testis, were not observed in non-testicular tissues. Of the 20 characterized genes, the testis-specific genes include Adad1, Dmrtc2, Luzp4, Prm2, Prss54, and Syce1, which may play a role in meiosis and/or spermatogenesis. Therefore, further research is required to elucidate the functional importance of these identified testis-specific genes in mouse male fertility.