The research was carried out on farms of the Bory Tucholskie Landscape Park near Tuchola. The aim of the research was to define the quantitative content of bacteria of Pseudomonas (the fluorescent subgroup), Arthrobacter, Azotobacter and the coryneform group in the rhizosphere of potato in different stages of its development. The “Aster” potato was grown in two farming systems: ecological and conventional. Microbiological analysis indicated that the bacteria of the coryneform group were the most numerous, and the next was Arthrobacter spp. More of investigated bacteria were isolated from the rhizosphere of potatoes grown in ecological farming system than in the conventional one. From the results obtained during three year’s study it is evident that the number of potentially antagonistic bacteria increased with the development of vegetation and was the highest in root zone area of the plants in harvest-mature tubers.