Abstract: In the end of 1994 the two different types of inactivatedvac-cines against HFRSC type I vaccine purified from tissue culture of Mongolian gerbils Kindney and type II vaccines prepared from tissue culture of hamster kidney)were immunizated in the crowd of three HFRS high-endemic areas in Jiangsu province.The booster of one dose of injection by the same tyep vaccine wascarried out in the crowd one year after primary immunization and efficacy of immune and protection was evaluatied druing 4 years period Results Showed The peak of positive rate of neutralizing antibody was after booster in the type I vaccine and then decreased trend was year by year.The rate was higher 4 years after primary immunization than one year;the peak of positive rate of neutralizing antibody was two weeks after primary immunization in the type II vaccine.the rate was higher 4 years after primary immunization (3 years after booster) than one year after primary immunization.In the same time of the different period the positive rate of im-munofluorescent antibody was higher in the type I vaccine than in the type II vaccine and the positive rate of neutralizing antibody was higher in the type II vaccine than the type I vaccine.During the 4 years period 4 cases occured in the immunized crowd of 3 cases occurred in the one year after primary immunization The serological type of the 4 cases were differed from the type of vaccine these results suggested:booster was necessary one year after primary imunization.The efficacy of protection of two types of vaccines were high special protection against the same case,the protection rate was 100%.the protection term was more than 4 years in the two types of the vaccines and alse.the antibody dependent immunization enhancement was not found by the observation.