Activity measurements of enzymes have been used in the research. Properties of microorganism populations of activated sludge have been estimated by this method. During the experiments, the activity of the following enzymes catabolising polyphosphate changes were measured: polyphosphatases, adenylate kinase, AMP:PP phosphotransferase. In order to designate the phosphorous release and uptake rate, a batch test has been carried out together with the activity measurement. Activated sludge for the experiments was taken from three substantially different wastewater treatment plants (WWTP). The enzymatic activities of the activated sludges which come from different WWTP indicate a high ability of microorganisms to change polyphosphates. The interpretation of the results shows good correlations of polyphosphatase and AMP:PP phosphotransferase activity with the phosphate release rate. The results of the experiments indicate the suitability of the activity measurement for defining potential possibility of a microorganism population to carry out biological phosphate removal by the activated sludge method.