GAMMA rays effect, on different dose levels on the production of ajmalicine as well as 5-phosphomevalonate kinase enzyme activety, was studied in Catharanthus roseus cell suspension cultures. The seedlings were taken from the young leaf puds and grown on MS solid medium for 7 weeks. Calli individual serially sub cultured by transfing to maintenance medium consisting of Gamborg's B5 medium. Cell suspensions were exposed to gamma rays after 4 weeks at dose levels of 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5 and 8Gy. Ajmalicine quantities were analyzed on VIS–spectrophotometer; also, the 5-phosphomevalonate kinase enzyme was particularly purified by ultrafiltration and activety analayzed, in addition, native PAGE electrophoresis was determined. 5-phosphomevalonate kinase enzyme bands and ajmalicine accumulation quantities were changed after the exposure to low doses from 1 to 6Gy, but the higher doses were lethal. The appropriated doses to activety of 5-phosphomevalonate kinase enzyme and Ajmalicine production were from 1 to 5Gy. Other dose levels (5.5 and 6Gy) did not affect on the 5-phosphomevalonate kinase enzyme activety and Ajmalicine production.