Abstract: In verification technology for arms control, age attribution of the plutonium is of far reaching importance for verification of nuclear warheads and surveillance of "Fissile Material Cut-off Treaty". According to decay modes of 241Pu, the variation with time of the ratio both the gamma rays and the atoms from the disintergration of the parent and the daughter nucleus is described in the paper. The results show that age of the plutonium could be evaluated by acquiring the atomic ratio of 241Pu and 241Am or measuring ratio of the gamma rays from 241Pu, 241Am and 237U.