We investigated the seasonality of myxomycete fruiting body formation under natural conditions in the field during four years in the Polistovo-Lovatskaya bog system (Northwestern Russia). It was shown that the species diversity of myxomycetes peaks in mid-summer and gradually decreases afterwards. The species composition of myxomycetes varies depending on the season. There were five phenological groups distinguished: summer, early autumn, late autumn, spring and species without pronounced periods of mass formation of fruiting bodies. It is shown the list of identifiable taxa may significantly vary in different years and there are widespread species that do not form sporophores every year. Thus, when conducting field studies, it is necessary to make observations over several years and throughout the entire snowless period.