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Soil-solution distribution coefficients, K d s, of I and IO s were measured by a batch method using 125 I for 68 wet (fresh) and autoclaved soils collected from upland fields, paddies, forests and open areas throughout Japan. Nine soil properties, such as soil-pH, cation exchange capacity (CEC), anion exchange capacity (AEC), active-Al (extractable Al by oxalic acid + ammonium oxalate) and total organic carbon (TOC), were also measured. The K d s for wet soils ranged widely from 1.1 to 10,200 1 kg"' for I" and from 2.1 to 8210 1 kg ' for 10,. The medians for I~ and IOi were 525 and 437 1 kg -1 , respectively. These values were almost two orders of magnitude higher than previously reported K d s for air-dried Japanese soils. The medians of K d s for I and IO, were the highest for Andosols, followed by Gley soils and Brown Forest soils. The K d s for sandy samples were low. Relatively good correlations (r > 0.65) were found between K d s for wet soils and TOC and total-N, indicating the contribution of organic materials on the sorption of I. The K d s were markedly reduced by autoclaving. The medians of K d s for autoclaved soils for I" and IO3 were 2.4 and 12.41 kg -1 , respectively. The effects of autoclaving on the sorption of I~ were more remarkable than those for It was estimated that 86% of I sorption and 50% of IOj sorption were attributable to the microbial activities and/or soil fractions which are sensitive to autoclaving.