This study was designed to examine saprophytic fungi diversity under different tree species situated in the same ecological context. Further, the link between the diversity and decomposition rate of two broadleaved, two coniferous and two mixed broadleaved-coniferous litter types was targeted. Litter material was decomposed in litter bags for 4 and 24 months to target both early and late stages of the decomposition. Fungal diversity of L and F layers were also investigated as a parallel to the litter bag method. Temperature gradient gel electrophoresis fingerprinting was used to assess fungal diversity in the samples. Mass loss values and organic and nutrient composition of the litter were also measured. The results showed that the species richness was not strongly affected by the change of the tree species. Nevertheless, the community compositions differed within tree species and decomposition stages. The most important shift was found in the mixed litters from the litter bag treatment for both variables. Both mixed litters displayed the highest species richness (13.3 species both) and the most different community composition as compared to pure litters (6.3–10.7 species) after 24 months. The mass loss after 24 months was similar or greater in the mixed litter (70.5% beech–spruce, 76.2% oak–Douglas-fir litter) than in both original pure litter types. This was probably due to higher niche variability and to the synergistic effect of nutrient transfer between litter types. Concerning pure litter, mass loss values were the highest in oak and beech litter (72.8% and 69.8%) compared to spruce and D. fir (59.4% and 66.5%, respectively). That was probably caused by a more favourable microclimate and litter composition in broadleaved than in coniferous plantations. These variables also seemed to be more important to pure litter decomposition rates than were fungal species richness or community structure.