Abstract: Studies were carried out on germination, pollen tube elongation, compatibility and radiosensitivity of giant pollen in ‘Zenjimaru' persimmon(Diospyros kaki L.f.). The results showed that: (1) the normal germination of giant pollen in stigma and medium indicated that giant pollen is compatibility with female parent; (2) the delayer germinant process and lower germination rate of giant pollen caused weaker competition in mixed pollination than normal pollen, which is the real reason of low rate of acquired triploids in breeding practice; (3) giant and normal pollen have different radiosensitivity, and giant pollen were lower. 1200 Gy was the fitter dose of radiation to stimulate giant pollen germination, meantime to restrain some normal pollen. Therefore, the competition of normal pollen could be increased in stigma. (4) the effect of post radiation could declined germination rate of giant pollen, and the germination could increased partly as the result of damage repair.