Due to the nuclear accident at Fukushima Daiichi nuclear power plant after the great East Japan Earthquake, wide area of land and sea have been contaminated by radio active isotopes. Among them, radioactive Cesium is an issues of great concern, because it will be long time recycled in forest ecosystems. We set fine (0.2 mm) and coarse (2 mm) mesh litter bags containing 16 g of mixed deciduous leaves (mainly Quercus serrata) at a deciduous forest in Fukushima, in December 2011. Weight loss, radio-Cs, total C, and N concentrations were monitored for one year. Radio-Cs concentration rapidly increased after April and reached its maximum on October in the both mesh bags, and it was 4 to 5 times higher than surface soil (0-5 cm) contamination. The coarse mesh bags showed ca. 20% higher concentration of radio-Cs than that in the fine mesh bags. Fungi are known as accumulators of K and Cs, thus we hypothesized that fungal growing on fresh leaf litter translocated radio-Cs from surface soil to litter layer. In the coarse mesh bags, there were more fungivorous microarthropods than in the fine mesh bags. Therefore, the fungal grazing by microarthropods may have enhanced Cs uptake by fungi.