Vanadyl ion is shown to form a bright green complex with thiosalicylic acid, [ o-mercaptobenzoic acid, (H 2SA)] with a characteristic λ max at 620 nm in the pH range of 4·0–7·0. Studies of this complex have been made using spectrophotometric, potentiometric and conductometric measurements. The results show the presence of a vanadyl-thiosalicyclic acid chelate in 50% aqueous alcoholic solution in the metal to ligand ratio of 1:2. The values of log K 1 and log K 2 have been found to be 10·24 and 8·39 respectively. This complex is also shown to form a chloroform extractable adduct with pyridine.