The objective of the paleoecological studies undertaken in the "Klocie Ostrowieckie" reserve was mainly to reconstruct the subfossil mire vegetation at a local and regional scale. This article presents the results of palynological and plant macroremain analyses of this site, and belongs to the first published studies of such a type, made in the Drawieński National Park. Based on our studies, five phases in the history of the mire development were determined. The most pronounced feature of that history, was a decline of Cladietum marisci clearly concurrent with a strong yet puzzling expansion of pine stands occurring approximately 1000 years ago.