The present study was undertaken to compare the viability and infectivity ofCryptosporidiumparvum oocysts that had been stored for 1,4,7,10,13,16,20,25 and 30 months at4℃ in 2.5％ potassium dichromate(Cr) and chlorinated tap water,respectively. An excystationprotocol was performed in vitro to evaluate viability. One hundred and eighty female BABL/c micewere used to evaluate the infectivity of oocysts by detecting the prepatent period of C. parvuminfection,the quantity of oocysts excreted,and the number of parasites that colonized the villi of theileum. The results showed that C. parvum oocysts preserved in Cr for 1-16 months and in water for1-13 months were capable of excystation in vitro and infection of mice in vivo. The excystation ratesof oocysts and the prepatent periods in mice infected by oocysts stored in Cr and water were notsignificantly different(p>0.05),and there was a strong correlation between prepatent period andduration ofoocyst storage(Cr: Re=0.92； water. R2=0.98). There were no significant differences inoocyst shedding from feces or parasitism of the terminal ilea of mice by Cryptosporidia between thetwo storage media(p>0.05). In conclusion,C. parvum oocysts may be stored at 4℃ in water insteadof Cr for the purposes of laboratory research. However,the presence of viable C. parvum oocysts inwater is a severe challenge to the drinking water treatment industry.