Background – The humid montane forests on the eastern slopes of the Peruvian Andes are known for their high biodiversity and natural resources. While their incredibly rich plant and animal communities are still in the process of being discovered, the diversity of smaller organisms such as the Myxomycetes are even more scarcely known. In this work, we document the Myxomycete diversity in these montane forests and evaluate species abundance, occurrence by substrates, distribution, and seasonality, thus documenting population status and species ecology. Material and methods – The study was carried out at the Wayqecha Biological Station located in the Cusco region of Peru. Two sampling campaigns took place in late January (wet season) and early May (dry season) of 2018. We performed a species inventory and evaluated alpha diversity, assemblage similarity, and abundance of Myxomycetes within six 100 m2 plots. We documented variations of species richness and abundance between seasons as well as between substrates. Results – We recorded a total of 81 taxa of Myxomycetes. The order Physarales was the most diverse, and the most abundant species were Didymium squamulosum and Diderma deplanatum during the wet and dry season, respectively. The substrate with highest diversity overall was dead leaves. Diversity was similar in both seasons but with a notable species turnover. Conclusion – The humid montane forest on the eastern slopes of the Andes in Peru revealed an unexpected richness in Myxomycetes. Based on our results, we conclude that this type of forest harbours one of the greatest Myxomycetes diversities in the Peruvian territory, also due to the important seasonal species turnover.