The rational utilisation of sludge as organic matter application into the soil permits enrichment in nutrients such as nitrogen and phosphorus. As dairy sewage sludge contains large amounts of organic matter and minerals, utilisation of such sludge in agriculture appears to be a noteworthy proposal. However, such waste can also be a source of toxic substances, heavy metals, inhibitors, xenobiotics and potentially pathogenic microorganisms. Therefore, it is so important to monitor its microbiological and biochemical properties in aspect of the safety for human health, natural environment preservation and a suitable level of agricultural production maintenance. The objective of study was the estimation of selected microbiological, biochemical and chemical properties of activated sludge (AS) and waste activated sludge (WAS) originating from the dairy sewage treatment plant. Nitrification and ammonification rates, respiratory, dehydrogenases, acid phosphatase, alkaline phosphatase, protease and urease activities were at significantly higher levels in the WAS than in the AS. The pH value of the AS and WAS oscillated within the range of neutral reaction.