Cryptosporidium parvum oocysts and Giardia 1amblia cysts were chlorine-resistant pathogenic microorganisms and were not treated effectively by a single step application of comrnon chlorine- bases disinfectants. Studies on altemative disinfection processes such as gamrna ray and E- beam for chlorine- resistant pathogenic microorganisms have been performed. The disinfection efficiency of B, subtilis spore after gamma ray was 99.4% at 2kGy, C, parvum oocysts treated with E- beam was observed with Transmission Electron Microscope. The results showed that the radiation technology is very effective for the disinfection of protozoa such as Cryptosporidium parvum.