Aim: It was aimed in this study, to investigate its antimicrobial effect on standard strains and clinical isolates of Hypericum capitatum var capitatum (H. capitatum) and to determine the phenolic content and antioxidant activity plant. Material and Methods: The antimicrobial effect of H. capitatum on standard bacterial strains and colistin-resistant ) Acinetobacter baumannii (A. baumannii) and Multi Drug Resistant (MDR) A. baumannii clinical isolates were determined by broth microdilution test (MIC) (ISO,2006). The total phenol content of the H. capitatum extract, of which some contents were clarified by, was investigated in seed, stem, and leaf samples. Antioxidant activity was determined by the DPPH (2,2-diphenyl-1-picrylhydrazil) method. Results: The plant extracted with methanol was found to have antimicrobial activity against Gram (+) bacteria (Staphylococcus aureus ATCC-29213 and Methicillin resistant S. aureus (MRSA) ATCC 43300 with 16 mg/mL). The efficacy against resistant A. baumannii clinical isolates was found to be effective between 64-128 mg/mL. The contents of the seed part of the H. capitatum plant by High liquid pressure chromatography (HPLC) method, were determined as shikimic acid (1720.42 ppm (mg/ml), Caffeic acid (52.50 ppm (mg/ml), Cinaminic acid, (14,217.61 ppm (mg/ml), Rosmarinic acid (30.90 ppm (mg/ml)) respectively. According to the H. capitatum plant parts, it was determined that the total amount of phenolic substances differed in the form of leaves (155.93 mg/L), stem (177.85 mg/L), and seeds (344.22 mg/L). Inhibition activity of DPPH was determined; seed (55,476%mg/mL), stem (57,318% mg/ml), leaf (53,241% mg/ml), BHA (Butyl hydroxy anosyl) and BHT (Butyl hydroxy toluene), respectively (93.77% and 88.62%) and ascorbic acid (95.21%). Conclusion: The antioxidant activity results of H. capitatum, which was found to be rich in phenolic content, demonstrated that methanol extracts of different plant parts are a natural antioxidant source that moderately scavenges free radicals. When the antimicrobial efficacy results were evaluated, it was observed that its efficacy against standart strains and resistant A. baumannii isolates, which are known to be difficult to treat clinically, is promising.