Abstract: Irradiating experiments on freshwater and seawater cultured pearls using electron accelerator have been done, and lots of colour changed samples have been obtained in the experiments. In the irradiating experiments, different types of cultured pearls with different colours and different conditions are used in order to get various treated samples and ideal condition. The colour produced by irradiation is stable, and the treated pearls are free of residual radioactivity. Natural aragonite and calcite crystals have also been treated in irradiation in order to investigate the colouring mechanism. After systematically comparing the features before and after treatment, the identification features are concluded and the colour change mechanism is discussed. The authors think that the radioactivity chemical reaction of organic substance and water in irradiation will be responsible to the colour change together with the oxidization of manganese.