Lactate dehydrogenase (LDH) is a ubiquitous enzyme that plays a significant role in the clinical diagnosis of pathologic processes. Discovery of the LDH (BmLDH) gene in B. mori may shed light on its role in the biology of Lepidoptera species, and afford further understanding of the function of the enzyme. In this study, we used the bioinformatics tools to identify LDH gene in B. mori. Sequence analysis showed that BmLDH cDNA contains a 996 bp open reading frame, encoding 331 AA proteins, with seven introns. Compared with hHLDH (human heart LDH), BmLDH contained the same key active sites. Domain search and protein fold recognition analyses provide compelling evidences that the deduced protein is a LDH. Using the computer program MEGA3, we conducted a search for homologs of BmLDH among many eukaryotic species and confirmed that the BmLDH was conserved in all organisms investigated. This gene has been registered in GenBank under the accession number EU000385.