Analytical method for the determination of129I and127I in environmental samples has been developed by using radiochemical neutron activation analysis. The129I levels in the samples such as soil (0.9–41 mBq/kg), precipitation (0.002–0.11 mBq/kg), pine needles (1.2–32 mBq/kg) and seaweed (<0.1–17 mBq/kg) collected near the nuclear facilities in Tokaimura were higher than those from the other areas in Japan. The highest129I concentration was found in surface soil (0–5 cm), and the highest129I/127I ratios were found in pine needles and precipitation. The129I/127I ratio was higher in rice paddy soil than those in wheat field soil collected around Tokaimura, while the concentration of129I somewhat higher in wheat field soil.