The effects of liming by CaO and CaCO 3 on soil microbial characteristics were studied during laboratory incubation of long-term contaminated arable and grassland soils from the vicinity of lead smelter near Příbram (Czech Republic). The CaO treatment showed significant negative effects on soil microbial biomass C and its respiratory activity in both studied soils, despite the fact that microbial biomass C in the grassland soil increased sharply during the first day of incubation. The metabolic quotient (qCO 2 ) in soils amended by CaO showed greater values than the control from the second day of incubation, indicating a possible stress of soil microbial pool. The vulnerability of organic matter to CaO could be indicated by the availability of K 2 SO 4 -extractable carbon that increased sharply, particularly at the beginning of the experiment. The amendment of soils by CaCO 3 moderately increased the soil microbial biomass. The respiratory activity and qCO 2 increased sharply during the first day of incubation, however it is not possible to ascribe them only to microbial activities, but also to CaCO 3 decomposition in hydrogen carbonates, water and CO 2 . The pH values increased more sharply under CaO treatment in comparison to CaCO 3 treatment. The improvement of soil pH by CaCO 3 could be therefore more convenient for soil microbial communities.