Testis-specific genes are essential for the spermatogenesis in mammalian male reproduction. We have identified a novel gene, Tsc24, from the results of the Affymetrix Genechip analysis in the developmental stage of days 4, 9, 18, 35, 54 and 6 months of postnatal Balb/C mouse testis. The scaling signal intensities of Tsc24 in the six stages of mouse testis showed that the expression of Tsc24 was not detected on day 4, 9 or 18 but on day 35, 54 and 6 months. The full cDNA length of mouse Tsc24 was 899 bp, with a 624 bp open reading frame encoding a 207 amino acid protein with a predicted molecular weight of 23.997 kDa. The results of semi-quantitative RT-PCR showed that the expression of mouse Tsc24 can only be detected after the mouse was 35 d old and the expressing level increased gradually from day 35 to 6 months. Of the eight tissues (liver, spleen, heart, lung, brain, kidney, epididymis, and testis) examined in mice, and of the 12 tissues (liver, kidney, muscle, brain, spleen, adipose, lung, heart, epididymis, testis, ovary and uterus) examined in human, Tsc24 was exclusively expressed in the testis, but in none of the other studied tissues. The result of subcellular localization of GFP-Tsc24 fusion protein in Cos-7 cells supports that Tsc24 protein is expressed in nuclear. Our study should be a basis for function characterization of the Tsc24 gene, leading to the elucidation of the molecular events underlying mammalian male reproduction.