Thiosemicarbazones and isothiosemicarbazones are of great interest due to their ability to coordinate to the transition metal ions and because of their interesting biological properties. Previously, 2-hydroxybenzaldehyde 4-allyl-S-(methyl/ethyl)isothiosemicarbazones and their coordination compounds have been reported.1,2 In this work 2-hydroxybenzaldehyde 4,S-diallylisothiosemicarbazone (HL) and 5 new copper(II), nickel(II), cobalt(III) and iron(III) coordination compounds with it are presented.formulaThe purity and structure of the synthesized isothiosemicarbazone was determined using NMR spectroscopy. Copper and nickel coordination compounds were synthesized by reaction between ethanol solutions of isothiosemicarbazone HL and corresponding copper(II) and nickel(II) salts in a 1:1 molar ratio, while cobalt and iron coordination compounds have been synthesized in a 2:1 molar ratio. The composition of the synthesized complexes: Cu(L)X (X=Cl-, NO3 -); Ni(L)(OAc); Co(L)2Cl; Fe(L)2NO3. The antioxidant properties of the synthesized substances have been studied using ABTS+• method. The concentration of semimaximal inhibition (IC50) of the isothiosemicarbazone HL toward these radical cations is 27 μM. Meanwhile the obtained coordination compounds manifest higher antioxidant activity with IC50 values 7-14 μM.