The Japanese encephalitis virus (JEV) serocomplex-group consists of mosquito-borne flaviviruses, which include West Nile virus (WNV) and JEV, and both may cause severe encephalitis in humans. WNV has spread rapidly across the United States since its introduction in 1999 and its geographical distribution within the western hemisphere is expected to further expand, whereas, JEV is the most common cause of viral encephalitis in Southeast Asia, China and India. Currently, there is no registered human vaccine or specific therapy to prevent or treat WNV infection. Here we describe the efficacy of recombinant domain III (DIII) of WNV glycoprotein E in a mouse model. It induces high neutralizing antibody titers, as well as, protection against lethal WNV infection in C57BL/6 mice. This vaccine preparation also afforded partial protection against lethal JEV infection.