Armillaria mellea root rots cause extensive economic losses on crops and in forest. Currently available chemical fungicides are ineffective in controlling the disease. Biological control, either alone or integrated with agronomic approaches may have better perspectives. Abiotic factors may affect biological control by influencing the activity of the biocontrol agents and the susceptibility of soil-borne pathogens to microbial antagonism. The effect of temperature on antagonism of Trichoderma spp. against A. mellea was evaluated in soil microcosms. Five plugs of A. mellea mycelium and rhizomorphs, protected by sterile lens tissue, were put between two layers of 200g of sieved sterile soil inoculated with 106 conidia of the testing microorganisms (T. atroviride SC1, T. virens TG1 or T. rossicum TG5) in polypropylene bottles (microcosms sets). Microcosm sets were maintained for seven days at 10 and 20°C. Antagonistic effect was evaluated as percentage of pathogen’s growth failure on malt extract agar (reduction of vitality). Trichoderma spp. isolates varied in their antagonistic abilities to parasitize A. mellea and the antagonism was highly affected by temperature. Antagonistic ability of T. atroviride SC1 was low at 10°C, while the other two isolates were inactive against A. mellea at this temperature. Conversely at 20°C pathogen vitality was significantly reduced by the presence of each tested microorganism (Tukey’s test, P = 0.05). Consortia of isolates did not increase global antagonistic ability at 10°C. Soil temperatures can differentially influence the antagonistic ability of microorganisms and this aspect is crucial in a view of climate change and increasing temperatures