Habitat requirements of two dormice (Gliridae) species were assessed in mature 75–180 years old mixed forest stands, according to correlations between nestbox use and habitat parameters measured within 2500 m2 areas around nestboxes. Use of nestboxes by the common dormouse (Muscardinus avellanarius) was positively related to the cover and number of hazel (Corylus avellana), number of honeysuckle (Lonicera xylosteum) plants, number of logs lying on the ground and age of forest stands, and correlated negatively with the number of coniferous trees forming the tree canopy. Use of nestboxes by the fat dormouse (Glis glis) was positively correlated with the total cover of oak (Quercus robur) trees, and negatively with the number of logs lying on the ground and number of dead trees and trunks. The two sympatric dormouse species showed different habitat requirements. Muscardinus avellanarius preferred thinner forest stands with well-developed understorey, while Glis glis preferred denser forest stands with well-connected tree canopies. Comparing their use of nestboxes suggested that mature forest stands were much more suitable for G. glis than for Muscardinus avellanarius. However, living conditions for M. avellanarius become better when mature forest stands thin out naturally, and understorey develops in gaps formed in the forest.