Abstract Mushrooms and substrata collected from a coastal pine forest in Rokkasho-mura, Aomori Prefecture, Japan were measured for radiocaesium and stable Cs. The ranges of 137Cs and stable Cs concentrations in mushrooms were ND-570 Bq kg -1 fresh weight and 0·005–1·6 mg kg -1 fresh weight, respectively. Both 137Cs and stable Cs concentrations in mushrooms were higher than those in common agricultural plants. The concentrations of 137Cs and stable Cs in the substrata were 37–261 Bq kg -1dry weight and 0·29–0·98 mg kg -1 dry weight, respectively. The specific activities of 137Cs in mushrooms were several times higher than those in the substrata. The substratum-to-mushroom transfer factors of 134Cs, 137Cs and stable Cs were in the range of 0·1–3·5, 0·03–3·3 and 0·01–1·7, respectively. These transfer factors were 1–3 orders of magnitudes higher than those for plants. The transfer factors of 137Cs were equivalent to those of 134Cs and were also significantly correlated to those of stable Cs.