A method in which90Y the daughter product of90Sr decay is extracted by tributyl phosphate (TBP) from ashed powdered milk is described. The90Y which is in equilibrium with90Sr is back-extracted into the aqueous phase and coprecipitated with milligram amounts of ferric hydroxide. The proposed procedure makes it possible to obtain thin planar sources convenient for low level gas counters. The overall detection efficiency of 45.5% for90Y (including chemical recovery of yttrium) was achieved. The detection limit for 200 g powdered milk samples and 10 000 s counting time was 0.065 Bq·kg–1. The concentration of90Sr in three-year old samples (after Chernobyl accident) ranged from 0.81 to 1.31 Bq·kg–1.