Beneficial effects of silicon fertilization (Si) have been observed in grass plants (silicon “accumulator” plants) especially under biotic or abiotic stress. The agricultural use of metallurgy slag, rich in silicon, represents a viable alternative for reducing waste impacts on environment and for soil-plant system, are taken advantage the material characteristics, leading to soil acidity correction, uptake in levels of calcium and magnesium, increase in availability of phosphorus, iron and manganese, reduction of aluminum toxicity. Plants tolerance to unfavorable conditions, especially drought, has been associated to enzymes accumulation in leafs, as a regulatory mechanism of physiological changes in plants, leading consequently to development of oxidative processes, through the proline accumulation (a regulatory mechanism of water losses in plants), besides the formation of reactive oxygen species (ROS): superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) antioxidant enzymes. The aim of this work was to evaluate the effect of Si application, from metallurgy slag, and drought tolerance in Brachiaria decumbens and Brachiaria ruziziensis plants, taking into account their biochemical parameters. The experiment was conducted in a greenhouse, in the Soil Science Department, São Paulo State University, Botucatu, Brazil, in a completely randomized factorial design, with five doses of Si (0, 242, 484, 968 and 1452 kg ha^-1) and three water management systems, corresponding to irrigate when soil water tension reached -0.0232, -0.0484 and -1.5 MPa. Were evaluated the total concentration of proline and the activity of superoxide dismutase, catalase and ascorbate peroxidase enzymes in plant extracts. The analysis are been executed, and at the present moment, the data have not been fully generated. Thus, the results will be disclosed at the time of sending the full summary.