The paper studies the effect of gamma radiation on the activity of cholinesterase enzyme . The results showed that a change in the activity has occurred in the studied absorbed dose range from 10 KGy to 100 KGy . Proposals to interpret the variation of activity of irradiated cholinesterase enzyme in the studied doses are given . Moreover the effect of time after the radiolysis process on the activity of the enzyme is shown . The final conclusion suggests the replacement of gamma irradiation radiotherapy by alpha or beta radiation for local treatment of tumors to reduce the radiation noxious effects on intact cells and enzymes