Radiocesium deposition on the ground and its impact on plants of a mountain forest. This study analyzes, for the first time, the impact of radiocesium deposited on the ground on the flora of a montane forest. Radiocesium is emitted by the nuclear power plant accident at Fukushima Daiichi nuclear power plant, which occurred in Japan in March 2011. In mid-September 2012 we studied five sites on the ground, where radioactive isotopes had deposited and not been removed by winds. We identified radioactive cesium deposited in the litter of each studied site and made measurements of the 137Cs in the leaves of five tree species, each one associated with a different litter type. We found that the radioactivity of the ground vegetation was higher at sites that are highly affected by atmospheric erosion. This effect is stronger with increasing soil depth. The mean values of total Km for 137Cs for the forest vegetation were 3.12 Bq g(-1) in organic litter, 1.07 Bq g(-1) in mineral litter and 0.16 Bq g(-1) in soil. Although the 137Cs concentration in the plant leaves ranged from 0.14 to 1.1 Bq g(-1) dry weight, most of the 137Cs in all trees was concentrated in the litter and mineral litter. The data obtained is an important step in the knowledge of the migration of radionuclides in forest ecosystems and could be used to estimate the radioactivity, particularly for 137Cs, in the terrestrial food chain. This result is important for developing a better model of the dispersion of radioactive cesium around the NPP.