A gene, presumably involved in spermatogenesis, was identified and characterized by using cDNA microarray. Hybridization intensity was 2.13 fold higher in adult testis than that in fetal testis. The full length of this gene was 4288 bp and it encoded a 578 amino acid protein. Conserved structure and amino acid sequence analysis revealed that the protein contained 1 Thif-domain, 2 UBACT-domains, and a functional active site cysteine lay upstream of UBACT domain, all of them also existed in ubiquitin-activating enzyme E1 and E1 like proteins. So we named this gene as a novel ubiquitin-activating enzyme E1 like gene (nUBE1L). Expression profile showed that nUBE1L was predominantly expressed in testis. Comparison of the expression of nUBE1L in different developmental stages of testis indicated that it was highly expressed in adult testis. In conclusion, nUBE1L is a novel human E1 like gene highly expressed in adult testis, which plays key role in ubiquitin system, and accordingly influences spermatogenesis and male fertility.