Mad honey is a complex mixture of numerous chemicals produced by honeybees from Rhododendron flowers. Consumption of mad honey leads to diarrhea, perspiration, dizziness, changes in consciousness, syncope, diplopia, as well as blurred vision, hypotension, and bradycardia due to the presence of grayanotoxins (GTXs). Therefore, it is important to detect the level grayanotoxins in mad honey. Besides its toxicity, mad honey also has antioxidant activity. This study was designed to determine the level of grayanotoxin-III toxin and antioxidant activity of ten different mad honey samples collected from the Black Sea region of Turkey. Liquid chromatography-tandem mass spectrometry was used for the quantitation of grayanotoxin-III. Antioxidant activity was evaluated using total phenolic contents, total ferric reducing antioxidant power, scavenging of 2,2-diphenyl-1-picrylhydrazyl and 3-(2-pyridyl)-5, 6-diphenyl-1,2,4-triazine-4',4''-disulfonic acid radicals. Quantities of grayanotoxin-III levels ranged from 68.754 to 0.701 mu g grayanotoxin-III/g honey. Mad honey MH7 from Artvin/Hopa had the highest grayanotoxin-III level. Although there were varying levels of grayanotoxin-III, mad honey samples were outstanding in terms of antioxidant activity. MH3 had the highest antioxidant potential. Although toxicity effect comprises, a metered dose of mad honey might also be explored as a potential source in clinical trials due to high bioactivity levels.