In this study, the microbiological properties, physicochemical characteristics, antimicrobial and antioxidant activities of Turkish commercial kefir products were investigated. The enumeration of Lactococci, aerobic lactobacilli, anaerobic lactobacilli, acetic acid bacteria (AAB) and yeast were performed by spread plate technique and counted as 7.35, 6.62, 6.85, 6.24 and 2.35 log CFU/g, respectively. Antimicrobial activity of kefir was evaluated using the disk diffusion method. Ten microorganisms, including seven Gram-positive strains and three Gram-negative strains were tested. While Listeria monocytogenes, L. ivanovii and Escherichia coli were the sensitive bacteria for all kefir samples, L. plantarum, Staphylococcus aureus, Bacillus cereus and E. coli O157:H7 are the resistant bacteria. The means of pH, total phenolic content, Trolox Equivalent Antioxidant Capacity (TEAC) and lipid peroxidation were 4.03, 4.39 mg GAE/100 mL, 0.15 µmol Trolox/mL and 7.23%, respectively. From the beneficial health properties point of view, kefir appears to be a promising food.