Abstract: A study on immunity duration post infection with Shigella was carried out in two villages of Changge county in 19761979．Bacteriological diagnosis WaS maintained in all cases of diarrhoea oecnred during JulySeptember of each year．During this period，776 cases of Shigd- losis(576 case5 caused by Sh．flexneri)were identified．Of them，94 cases were reinfected．Rein-fection with homoserotype such as Sh．Ihxneri，dysenteriae 2，Sh．boydii and Sh sonneri was not seen in 13 months after the first infection，but reinfection caused by homoserotypes of the pre-dominant epidemic serogroup of Sh．fhxneri could happen in 915,2127，3339 months later and the reinfection caused by homoserotypes of Sh．dysenteriae2 and Sh．sonneri were also hap-pened in 2127 or 3339 months later．Reinfection，however，with heteroserotypes or heter-groups of Shigella could Occur in 13 months after the first infection．There was no significant difference of incidenee between the persons infected with the same serotype 9～15 months before and noninfected．The data showed that the duration of serotype or group-specific immunity mightpersistend about one year after natural infection.