Environmental stresses are the most limiting factors for agricultural productivity. Resistance to abiotic stresses is considered the one of the desired traits of crops. The various tolerance mechanisms have been suggested on the basis of the biochemical and physiological changes related to drought. The water deficit may incite the formation of free radicals of oxygen. When the ROS overcome the critical threshold concentration, they cause oxidative damage of cellular components, plant senescence and premature death of plant. A plant protection from excessive production of reactive oxygen species (ROS) may include the enzymatic decomposition and the inactivation (neutralization) by low molecular weight compounds. Recently a lot of research has been devoted to the prospecting of compounds with antioxidant properties and argumentation of their use on reasons of increased ROS detoxification and protection from oxidative stress. The objective of this study was the assessment the antioxidant propriety of a [Co(DmgH)2(Thio)2]NO3 (Coditiaz) and its effect on the maize plant tolerance at drought conditions. Greenhouse experiments were performed on plants grown under controlled soil water content. The analyses were performed at the critical period of plant development – the stage of "panicle-flowering". The experiment design included the two treatments: a) control plants, grown at permanent favorable soil water content; b) plants exposed to the drought for 10 days. Parallel variants included the plants treated by 0, 0005% water solution of Coditiaz. It was shown, that ROS generated during the drought induced lipid peroxidation in cell membranes of leaves. The treatment of plants with Coditiaz at optimal soil water content provided a reduction of malondialdehyde (MAD) content compared to untreated control plants. In contrary, the MAD content in leaves of plants exposed to drought stress increased significantly, however, to a lesser degree in treated plants with coordination compound. The tolerance of plants to water stress was closely associated with its antioxidant enzyme system. A high activity of enzymes superoxide dismutase, catalases, ascorbate peroxidase, glutathione peroxidase, glutathione reductase and gwayacole peroxidase was specific for plants treated with Coditiaz. The ascorbic acid and carotenoids are known also essential for plant protection from excessive ROS production. In our study, the ascorbat and carotenoids contents decreased in the leaves of plants under drought stress. Pigment content showed that typical oxidative stress, caused by drought, leads to a significant chlorophyll a, b and carotenoids decrease, less pronounced to the treated with Coditiaz plants. The results indicated that water deficit stress during reproductive development resulted in significant decreases in leaf stomatal conductance, transpiration and photosynthesis. This led to decrease water use efficiency for plant biomass accumulation. Application of Coditiaz is to mitigate the negative consequences of water deficit stress on maize gas exchange functions, indicating that either from the leaves is minimal under conditions of drought. The tolerance of maize plants to oxidative stress, caused by drought, is closely associated with its antioxidant enzyme system and with low-molecular weight antioxidants, such as ascorbate and carotenoids. Application of Coditiaz has a protective effect from the oxidative destruction of photosynthetic pigments and of gas exchange functions. Coditiaz revealed the antioxidant properties and could have an important role in protection against drought.