Hantavirus are rodent-borne RNA virus that belongs to the family Bunyaviridae. Those viruses persistently infect a variety of rodents, and are transmitted by aerosols of their urine, feces and saliva. Antibody titers of sera obtained from normal laboratory rodents against hantaviruses were investigated by indirect immunofluorscence antibody technique (IFA), Seroconversion rates of normal laboratory rodents showed higher in rats than that from hamster and mongolian (M). gerbil. Theses rates of normal laboratory rodents also showed higher in titers against puumala virus (PUUV) than in hantaan (HTNV) and seoul virus (SEOV). We are concerned about infections caused by hantaviruses, especially by PUUV, occurred in laboratory rodents.