Mobile forms of radionuclide ¹³⁷Cs in different soils (natural pastures) of northeastern Poland was evaluated. An attempt was made to show if and what mobile forms of ¹³⁷Cs is related to different soil properties. For this reason 108 soil samples from 0 to 10 cm in depth were measured for mobile forms of ¹³⁷Cs activity and analysed for clay fraction, pH-value, exchangeable potassium (Kex.), exchangeable calcium (Caex.), magnesium (Mgex.), sodium (Naex.) content, organic matter and organic carbon content (C org.), cation exchange capacity (CEC). Samples of soils were collected in the period from June 1995 to July 1996. The radiocaesium and mobile forms of ¹³⁷Cs activity were determined by gamma spectrometry. The mobility of ¹³⁷Cs was studied by means of sequential extraction. Mobile forms of radionuclide ¹³⁷Cs were related to physicochemical parameters of soils.