The presence of pathogenic microorganisms in sewage sludge is one of the crucial factors affecting their use in agriculture and in nature. An appropriate method of sludge hygienization can contribute to the reduction of the presence of pathogenic microbes in the sludge or to their complete elimination. This study presents the possibility of using dry ice in the hygienization of surplus activated sludge. The scope of survey covered microbiological as well as physiochemical analyses of the sludge. The microbiological analyses conducted show the hygienization effect of dry ice on surplus activated sludge such as the reduction of the total number of bacteria as well as of pathogenic bacteria. In the case of sludge to dry ice 1:1 voluminal ratio, the total number of bacteria has been reduced by 76%, the number of