The antibacterial effect of wild-growing Juniperus sibirica Burgsdorf and Juniperus sabina L. var. sabina essential oils was studied in a microtitre plate-based MIC assay. Bacterial growth was monitored by measuring turbidity of the sample (OD600), as well as by following the colorimetric resazurin reaction. Essential oils were prepared from the needles of female plant samples and analysed by GC-MS. Hydrocarbon monoterpenes were determined as the dominant constituents; the compounds detected in the highest amounts were α-pinene (74.5%) and sabinene (54.3%) in J. sibirica and J. sabina oil, respectively. As indicator strains in the MIC assay, we used selected Grampositive (Enterococcus faecalis ATCC29212, Staphylococcus aureus ATCC25923, Bacillus subtilis ATCC6633 and Listeria innocua ATCC33090) and Gram-negative (Escherichia coli ATCC25922, Salmonella typhimurium ATCC14028, Salmonella enteritidis ATCC13076, Aeromonas hydrophila ATCC49140) bacteria. Bacterial inocula used in the MIC assay were adjusted to a 0.5 McFarland standard, corresponding to approximately 108 CFU/mL. The obtained results indicated that determination of turbidity decrease cannot be used to precisely quantify MIC values of the oils. The resazurin-incorporated MIC assay showed that the most susceptible strains were A. hydrophila and B. subtilis, with MIC values of 12.5 mg/mL and 6.25 mg/mL, respectively, for J. sibirica, and 6.25 mg/mL for both bacteria for J. sabina. The remaining bacteria were far less sensitive to Juniperus oils. In the range of tested concentrations, the effect of both oils was predominantly bactericidal, but J. sibirica oil showed a bacteriostatic effect against some Gram-negative bacteria.