Fifteen kinds of antibiotics both in liquid or dry stantes wre investigated for the purpose of radiation effect on the antibiotic activities after irradiation. In liquid states, the antibiotics such as amoxyllin, ampicillin, capharolidin and hetacillin were inctivated 90% of their antibiotic activities at radiation doses of 50Krad, and penicillin, dicloxacillin, caphalothin, cloxacillin, erythromycin and caphalexin and kanamycin were decomposed at radiation doses of 1.5Mrad, respectively. In dry states, all antibiotics were stable at radiation doses of 5Mrad. On the other hand, the neomycin in liquid state was rather increased the antiboctic activity about 1.2 and 8 times when the E. coli ATCC 113-3 and B. subtitilis ATCC 6633 were used aas a standard microorganisms, whereas, the decrensed antibiotic activities were observed in S. typhi Ty-2(36.2%), St.faecium(10.79%), B.sphaericus CIA(9.066%) and St.aureus ATCC 6538p(70%).