Methanol and aqueous branch extracts of five Juniperus species were examined for their effects on Staphylococcus aureus ATCC 6538P and S. aureus 810 biofilm. The Turkish plant material was Juniperus communis L. var. communis, J. communis L. var. saxatilis Pall., Juniperus drupacea Labill., Juniperus oxycedrus L. ssp. oxycedrus, J. oxycedrus L. ssp. macrocarpa (Sibth. & Sm.) Ball. The Juniperus extracts were subjected to preliminary phytochemical analysis by thin-layer chromatography. The antimicrobial activity was evaluated using the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC). The effects of the extracts on biofilm formation and preformed biofilm were quantified by both biomass OD and the CFU counting method. The phytochemical screening revealed the presence of polyphenols, coumarins, lignans, steroids, alkaloids and terpenes. For both strains, the MICs of all extracts were in the range of 4.88-78.12 microg mL(-1). On S. aureus ATCC 6538P, the effects of subinhibitory concentration (0.5 MIC) of the extracts were minimal on planktonic growth and on adhering cells, whereas they were greater on biofilm formation. Differently, on S. aureus 810, they showed only a rather low efficacy on biofilm formation. The extracts at 2 MIC demonstrated a good activity on a preformed biofilm of S. aureus ATCC 6538P.