Decomposition of cellulose to glucose requires complex cooperation of glycoside hydrolase enzymes. As a result of glycoside β-1,4 bonds hydrolysis, shorter chains of cellulose, oligodextrin, cellobiose and glucose are created. A number of bacteria and fungi demonstrate the capacity to degrade cellulose. Their activity can be assessed with the use of qualitative and quantitative methods. Qualitative methods with the use of e.g. Congo red, are used in screening studies, however, they do not provide information about the quantity of the produced enzyme. Spectrophotometric methods are more accurate and they measure the quantities of reducing sugars with the use of appropriate substrates, e.g. carboxymethylcellulose is used to determine endoglucanases, avicel cellulose to determine exoglucanases and Whatman filter paper to determine total cellulolytic activity. Activity of microorganisms depends not only on their species or type but also, among others, on substratum composition, cultivation conditions and the appropriate selection of parameters of the carried out enzymatic reactions.