The absorption coefficients of β-rays from UX2 and RaE were completely studied. Two outstanding features have been found by the authors: (1) The complete logarithmic absorption curve of β-rays is not a really straight line but a broken one consisting of several segments of straight lines which intersected at a certain point. The slopes of the segments are greater as the absorbing screens are thicker. (2) The values of the absorp-tion coefficients are not constant but can be varied according to the surrounding conditions of measurement. Among the conditions, the substance beneath the preparation Or the reflector, the substance encircles the preparation or the screen support, and the distance between the active preparation and the ionisation chamber window are the three main determinating tactors which influence the variation of the coefficient.