The changes in physico-chemical composition of mine water flowing out from the now closed Kivioli mine in 1988-1996 concerning sulfates, chlorides, calcium, magnesium, sodium, potassium and total hardness have been studied. Annual average values of these parameters are in a clear correlative function: the correlation coefficients lie within the range of 0.8367-0.9993. Considerable differences in the hydrogeological and geochemical processes running underground after closing the mine have caused up ro threefold decrease in the content of above-named components in the mine water. As a result, the mine water flowing out is relatively pure at the present time and does not essentially damage the quality of water in Purtse River any longer There is no oil and phenolic pollution in presently outflowing mine water whereas during the closing of the mine the isolation of the part of mine (pit bottom) that remained under the territory of Kivioli Oil Shale Processing Plant from all mined area, was accomplished effectively.