The effect of commercial enzymatic preparations on sewage sludge composting was studied. The process of composting was carried out in industrial conditions with addition of selected enzymatic preparations. The sludge was mineralized in aerobic conditions. It was found that when the tested preparations had been added, the mineralization of organic matter in the composted material was much improved. In a control prism in which no enzymatic preparations were added, more beneficial changes of factors that had an influence on fertilizing value were observed. The range of changes in the factors being analyzed show that the most intensive transformations are reported in the first 8 weeks of the process. After that period the intensity of transformations decreases significantly and differences in changes of the tested parameters are very small.The effect of commercial enzymatic preparations on sewage sludge composting was studied. The process of composting was carried out in industrial conditions with addition of selected enzymatic preparations. The sludge was mineralized in aerobic conditions. It was found that when the tested preparations had been added, the mineralization of organic matter in the composted material was much improved. In a control prism in which no enzymatic preparations were added, more beneficial changes of factors that had an influence on fertilizing value were observed. The range of changes in the factors being analyzed show that the most intensive transformations are reported in the first 8 weeks of the process. After that period the intensity of transformations decreases significantly and differences in changes of the tested parameters are very small.