Abstract: Nocardia seriolae is the main pathogen of fish nocardiosis. N.seriolae hydrolase (HYD) may be the virulence factor of N.seriolae. In this study, the results show that the N.seriolae HYD is not a secreted protein. Subcellular localization studies reveal that HYD-GFP fusion proteins uniformly distributed in whole FHM cell. Typical apoptotic features, such as nuclear pyrosis and apoptotic bodies, were found when HYD protein expressed in FHM cells according to subcellular localization and overexpression studies, while the quantitative assay of Caspase-3 activity shows that HYD did not increase the level of apoptosis significantly. The study lays foundation for further study on the pathogenic mechanism of N.seriolae.