Display omitted •We synthesized Ni(II), Fe(III), VO(IV) complexes of thiosemicarbazone and characterized.•The compounds were tested for in vitro antioxidant capacity using the CUPRAC method.•It was measured the scavenging activities of reactive oxygen species (ROS), also.•The ligand exhibited more potent in vitro antioxidant capacity than its complexes.•V(IV) and Fe(III) complexes had significant scavenging activity for ROS. The nickel(II), iron(III), oxovanadium(IV) complexes of the 3-hydroxysalicylidene-S-methyl-thiosemicarbazone (L) were obtained from the 3-hydroxysalicyldehyde-S-methylthiosemicarbazone with the R1-substituted-salicylaldehyde (R1: H, 3-OH) in the presence of Ni(II), Fe(III), VO(IV) as template ion. The ligand and its complexes were characterized by elemental analysis, electronic, UV/Vis., 1HNMR, EPR and IR studies. The free ligand and its metal complexes have been tested for in vitro antioxidant capacity by reduction of copper(II) neocuproine (Cu(II)-Nc) using the CUPRAC method. The ligand exhibited more potent in vitro antioxidant capacity than its complexes. The obtained trolox equivalent antioxidant capacity (TEAC) value of the iron(III) complex (TEACCUPRAC=3.27) was higher than those of other complexes. Furthermore, the antioxidant activity of the free ligand and its complexes were determined by in vitro methods measuring the scavenging activity of reactive oxygen species (ROS) including hydroxyl radical (OH), superoxide anion radical (O2−), and hydrogen peroxide (H2O2), showing that especially the V(IV) and Fe(III) complexes had significant scavenging activity for ROS.