Higher plants have different capacities to accumulate and tolerate selenium, referred to as accumulative and non-accumulative plants. Selenium-accumulators plants may contain hundreds of times more selenium than non-accumulators even when grown in the same soil, or can also grow in soils with low and medium selenium reserves; while selenium non-accumulator plants present low accumulation and tolerance to high selenium levels in the culture medium. Several studies have demonstrated the protective role of selenium in relation to oxidative stress in plants. Depending on the dose used, Se can activate certain enzymes such as superoxide dismutase, glutathione reductase and glutathione peroxidase. These enzymes are activated in the presence of Se, reducing the rate of lipid peroxidation and formation of hydrogen peroxide in plant tissue cells, which results in reduced senescence. Symptoms of selenium toxicity include reduced growth, chlorosis of leaves and pink coloration of the roots, yellowing of leaves and black spots. Studies provide evidence on a beneficial role of Se in plants and for environmental phytoremediation. However more research is needed to consolidate the beneficial effects of Se in plants. Key words: Selenium, accumulating plants, metabolism, functions plant, toxicity.