A method for using inactivated Japanese encephalitis virus particles as an adjuvant of a vaccine is provided. A method for using inactivated Japanese encephalitis virus (JEV) particles as an adjuvant of various vaccines or a mixed vaccine, said JEV particles being obtained by inoculating JEV Beijing-1 strain to Vero cells, culturing said JEV-infected cells to give cultured cells or culture supernatant, purifying JEV particles from said cultured cells or culture supernatant and inactivating said JEV particles with formalin, a method for preparing a (mixed) vaccine which comprises a step of letting inactivated Japanese encephalitis virus be contained, and a mixed vaccine prepared by said method.
