[en] Highlights: • We examined variation in vertical dissolved ¹³⁷Cs flux through litter. • Ratio of ¹³⁷Cs flux to litter inventory during the survey was less than 10%. • Spatial variation showed log-normal distribution and had 20–25 times difference. • Spatial variation was determined by litter ¹³⁷Cs inventory and canopy openness. - Abstract: We examined spatial variation in vertical ¹³⁷Cs flux from the litter layer using lysimeters combined with copper-substituted Prussian blue in two forests (deciduous broad-leaved and Japanese cedar (Cryptomeria japonica)), approximately 40 km northwest of the Fukushima Daiichi Nuclear power plant. The study ran from August 2016 to February 2017 in three periods; summer (10 Aug–4 Oct), autumn (5 Oct–30 Nov) and winter (1 Dec–27 Feb). Twenty-five and 15 lysimeters were installed in the deciduous broad-leaved and the Japanese cedar sites within 400 and 300 m² areas with 3–5 m intervals, respectively. The geometric means of the flux in the deciduous broad-leaved site were 0.51, 0.085 and 0.060 kBq/m²/month in summer, autumn and winter periods, respectively. In the Japanese cedar site, the mean fluxes were 0.45, 0.036 and 0.023 kBq/m²/month. The ratio of ¹³⁷Cs flux during the survey period to litter ¹³⁷Cs inventory was 6% and 1% on average in the deciduous broad-leaved and Japanese cedar sites, respectively. The ¹³⁷Cs flux in the summer period was much larger than those in other periods, resulting from higher precipitation in the summer. Our fine scale observation with 5 m interval showed very large spatial variation in the ¹³⁷Cs flux and the differences between maximum and minimum range from 8 to 104 times, but were mostly 20–25 times. The spatial variations in the ¹³⁷Cs flux were affected positively by those in the litter ¹³⁷Cs inventory and negatively by canopy openness.