Residues from araerobic digestion of mixs. of maize silage with slops or pig slurry were composted with straw. Changes of dry mass, org. matter content, humification and maturity indexes as well as contents of N, P, K, Mg and selected microelements were detd. The composting of solid fraction from digestate was found an effective method for treating digestate from biogas prodn. plants. The mature composts showed an applicability as good fertilizers.