Soil blocks were taken into culture boxes from 12 paddy fields within 5 km radii of Yonggwang and Ulchin NPPs and $^{90}Sr$ was applied to the surface water at a pre-transplanting stage and $1{sim}2$ days before the start of heading. Following the pre-transplanting application, transfer factors were investigated for $2{sim}4$ years. In the year of application, transfer factors $(m^2;kg^{-1}-dry);of;^{90}Sr$ applied before transplanting, showing no regionally distinguishable trend, varied with soils by a factor of about 2 with averages of $2.6{times}10^{-4}$ for hulled seeds and $1.3{times}10^{-2}$ for straw Transfer factors of $^{90}Sr$ applied shortly before heading were about 2 times greater than those applied before transplanting. Transfer factors tended to decrease with increasing soil pH and exchangeable Ca. Generic values of $^{90}Sr$ transfer factors in the year of deposition were proposed for the Korean paddy fields. In the second year compared with the first year, the transfer factor decreased more in Ulchin soils, which were on the whole higher in sand content, than in Yonggwang soils. For Yonggwang soils as a whole, the annual decrease in transfer factor was well described by an exponential equation with a half-life of about 2.2 years.
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