Chitinases (E.3.2.1.14) are ubiquitous hydrolases capable of cleaving the b-1,4-glycosidic bonds in chitin polymers. The physiological significance of these enzymes in the development and immunity of various animals has recently been reported [Badariotti F, Thuau R, Lelong C, Dubos MP, Favrel P. Characterization of an atypical family 18 chitinase from the oyster Crassostrea gigas: evidence for a role in early development and immunity. Dev Comp Immunol 2007;31(6):559–70]. Lampreys are regarded as the most phylogenetically primitive species that may have an adaptive immune system. However, no chitinase gene has yet been identified in lamprey. We report here the identification and characterization of a chitinase-coding gene from the lamprey Lampetra japonica. The predicted amino acid sequence of the chitinase gene consisted of a typical catalytic domain and a peritrophin-A type chitin-binding domain. Real time RT-PCR analysis showed that the chitinase gene was expressed in various tissues of adult L. japonica, particularly in the liver, where a significant difference between male and female was observed during the pre-spawning period. A significant increase in expression was also observed in vivo following stimulation by bacteria or fungi. These findings seemed to suggest that in L. japonica, chitinase probably plays an important role in gonadal development as well as in innate immunity in response to invasion by microorganisms.