Same results of a 5-year investigation of the radioactive contamination or mushrooms originating from the Western region of Ukraine are presented. Considerable variations of radiocaesium accumulation by mushrooms which belong both to different and the same species were noted. The corresponding radiocaesium transfer factors (a ratio of the caesium isotope content in mushroom and in soils at a given area) were calculated. For the mushrooms collected from the territory of the Shatsk National Natural Park (ShNNP, Volyn region) a sequence representing an increase of ¹³⁷Cs accumulation was complet sequence.