Antioxidant, antimicrobial and antibiofilm activities of potassium metaborate (KBO2) was investigated within the present study. Antioxidant capacity of potassium metaborate was determined by β-carotene bleaching (BCB) assay and hydroxyl radical scavenging activity. Potassium metaborate was evaluated for its antimicrobial effects against selected Gram-positive bacteria, Gram-negative bacteria and a yeast via broth dilution method. The inhibition capability of potassium metaborate on the microbial biofilm formation of tested microorganisms was measured by microplate biofilm method using MTT (3- [4, 5- dimethyl-2-thiazolyl]-2, 5-diphenyl-2H-tetrazolium-bromide). Biofilm inhibition capacity of potassium metaborate was also observed by Scanning Electron Microscope (SEM). Potassium metaborate was found to have the ability to scavenge hydroxyl radicals with an inhibition rate of 71.13% at 100 mM concentration. Antioxidant activity of potassium metaborate as determined by BCB assay gave higher result with an inhibition rate of 86.96% at the same concentration. According to the MIC (minimum inhibition concentration) values, the potassium metaborate inhibited the growth of C. albicans, S. aureus and E. coli at 62.5 mM concentrations while it was 31.25 mM for B. subtilis and 125 mM for P. aeruginosa. The highest antibiofilm activity was determined at the MIC of potassium metaborate with the reduction rate of 90.18% against C. albicans. It was concluded that, potassium metaborate have strong biological activities and can be effectively used for biomedical and environmental solutions.