The survival and establishment of a Trichoderma atroviride strain in three compost products were evaluated. Spent mushroom (Agaricus bisporus) compost at two different maturity levels (young and mature) and green compost from garden wastes were enriched with a sporal suspension of the antagonistic fungus. Peat moss and potting soli were used as controls. The population dynamic of T. atroviride was estimated at different times over a period of 140 d after enrichment. The potential toxic effect of enriched composts on the survival of the collembolan Protaphorura armata was also investigated. All compost products were suitable for the establishment of T. atroviride. Survival was the highest in mature spent mushroom compost. In particular, over the experimental period this compost product was able to sustain the population level of the antagonistic fungus obtained by enrichment. Moreover, mature spent mushroom compost promoted the highest level of rhizoplane colonisation ability of the antagonistic fungus. None of the tested products was toxic for P. armata specimens. Among microbial, physical and chemical parameters considered the survival of T. atroviride resulted only related to N form; the fungus seemed to survive better where NH4 was prevalent on NO3.