Soil fauna (macrofauna and mesofauna) were sampled in 13 beech forest stands of the Ardenne mountains (Belgium) covering a wide range of acidic humus forms. The composition of soil fauna was well correlated not only with humus form, but also with elevation, phytosociological type, tree growth, mineral content of leaf litter, and a few soil parameters such as pH and C/N ratio. The nature of the mechanisms that can explain these relationships is discussed in light of existing knowledge.