Inductively coupled plasma mass spectrometry (ICP-MS) has been applied to the measurement of plutonium isotopes in soils. In the ICP-MS, a calibration curve method was conveniently utilized even in high viscosity solution using a Babington nebulizer. Plutonium concentrations in soil around the Kashiwazaki-Kariwa nuclear power station were found to be in the range of 0.054 to 1.0 Bq/kg with an average of 0.27 Bq/kg. The ratios of 239Pu/240Pu were also obtained with the ICP-MS to investigate the origin of Pu-isotopes. On the basis of this result, the origin of the Pu-isotopes was attributed to be fallout from the past atmospheric nuclear tests.