We evaluated ¹³⁷Cs concentration of cedar litter, surface soil, and terrestrial insects in riparian zones and cedar litter and aquatic insect in streams after one and five years of Fukushima Daiichi Nuclear Power Plant (FDNPP) Accident for examining temporal change in a headwater catchment (170ha). The area was covered by Japanese cedar with initial deposition of 100-300kBq/m². All of the samples were collected for each season. Based on the data, we calculated ecological half-lives (T_eco). T_eco of terrestrial litter was 1.4 yrs, while the aquatic litter was 3.8 yrs. T_eco of terrestrial litter was similar value to the previous study in Finland (2.1 yrs). T_eco of terrestrial and aquatic insects were 1.8 and 2.6 yrs respectively. However, values of T_eco differed depending on functional feeding group with high in collector (7.2 yrs), low in shredder (2.1 yrs). Because of contaminated POM and fine sediment was accumulated in pools, high ¹³⁷Cs concentration of habitat and food for collectors affected high level of ¹³⁷Cs in their bodies after one to five years and resultant high T_eco value.