The changing of soil biological characteristics due to the addition of raw and composted sewage sludge (at 0, 1.5 and 3.0%) were evaluated during a 165-day incubation experiment. Generally, increasing the addition rate of sewage sludge and its compost up to 3%, total organic C content (TOC), cumulative organic C decomposition (COCD), biomass C and basal respiration in soil were significantly increased. The increase in biomass C and basal respiration were significantly higher in sewage sludge-treated soil as compared with compost-treated soil. By extending the incubation period, TOC content biomass C and basal respiration were significantly decreased and COCD was significantly increased The differences in biomass C/TOC ratio at the beginning and end of the incubation experiment were significantly higher in waste-amended soil as compared with the untreated soil.  Such differences were much higher when the soil treated with sewage sludge as compared to the soil treated with compost. At the beginning of the experiment, all values of metabolic quotient (qCO₂) in the waste-amended soil were significantly higher as compared with the untreated one. Sewage sludge-amended soil had usually greater qCO₂ values compared with compost-treated soil at the used two application rates. High positive correlations were observed between biomass C, basal respiration and the biomass C/TOC ratio. Any of these may be used as a bio-indicator of a soil biological activity after amendment by organic materials.