Abstract: Experimental results show that when the plants are exposed to enhanced UV-B radiation for 7～14 days．the activities of agrinine decarboxylase (ADC)，ornithine decarboxylase(ODC)and s-adenosylmethionine decarboxylase(SAMDC)in leaves are increased by 165．74％，104．60％and 89．60％in“Shan You63”(Sy63)，59．91％，41．30％and 23．68％ in“Nancheum”(NC)and 115．93％，14．45％and-33．01％in IR_65600.85，respectively．However，the three enzymic activities turn to decrease with the treatment time increasing(21～28d)and the decreased extents of ODC and SAMDC are much higher than that of ADC．The activities of ADC and ODC are increased by 89．72％ and 3．71％ in Sy63 and 73．95％and 27．38％ in NC exposedto UV-B radiationfor 21～28 days．The activity of ADC is alsoincreased by 94．41％ but ODC activity is decreased by 13．57％ in the leaves of IR_65600.85 compared with the controls．As far as SAM DC is concerned，the enzym ic activities in Sy63，NC and IR_65600.85 are reduced by 40．06％，19．20％ and 38．21％respectively when they are exposed to enhanced UV-B radiation for 21-28 days．The reverse is true in the case of polyamine oxidase(PAO)，indicating its lower activity in earlier treatment courses(7～14d)，but much higher activity in late courses(21～28d)compared with the controls．The in turn result in the increased contents of polyamine(PA)，espedally putrescine(Put)and the results of the experiment have shown their differences in diverse rice genotypes．