Studies considering hummocks and hollows structure of bog forests were carried out in the Stare Biele Reserve in the Knyszyn Forest. The aim of the study was better recognition of bog forests spatial structure including recognition of soil chemical composition of hummocks and hollows. The bog forest communities in Stare Biele Reserve have various percentage of hummocks. The hummocks have similar morphological structure and are distinctly separated from hollows in all four bog forest communities. Degree of hummocks development and their morphological structure have big impact on plant distribution on their surface. Soil chemical properties are one of the factors, which influence floral abundance and composition of microcenoses. Soil reaction and calcium content, among other measured properties, exert the biggest influence on the floral abundance and composition of microcenoses.