The production of mushrooms enriched with essential elements, e.g. selenium, for human health is an interesting strategy to improve the functional foods supply. The selenium is an essential mineral and makes part of structure of enzymes involved in the oxidative metabolism. However, the selenium effect on the activity of respiratory and lignocellulolytic enzymes has not been considered. The understanding of this effect is important to determine the selenium concentration that increases the mushroom productivity and the degradation rate of the substrate. In this study, it was observed reduction of the respiratory activity of Lentinula edodes (Berk.) Pegler, the shiitake mushroom, in function of the increasing of the sodium selenite concentration in the substrate (p < 0.05). Selenium did not inhibit the activity of the hydrolytic enzymes (cellulase and xylanase), but it increased the activity of the oxidative enzyme (laccase). Respiratory activity of L. edodes has a negative correlation with sodium selenite concentration added in substrate. Thus is important to define the ideal dose of selenium to be added to the substrate for increasing lignocellulosic residues degradation and, consequently, guarantee a higher production of Se-enriched mushrooms.