Abstract: Agaricus brasiliensis mycelium is rich in antitumoral molecules such proteoglycans and ergosterol and this is the first study to report production of mycelium and ergosterol by A. brasiliensis in solid-state fermentation. The aim of this research was to study the biomass content and several growth parameters of A. brasiliensis mycelium on grounded wheat grain as the substrate in solid-state fermentation with ergosterol as the main growth indicator. The growth parameters were determined by the respirometric activity in the columns of a bioreactor with forced aeration and the outlet air composition was determined by gas chromatography. Ergosterol was extracted, measured by liquid chromatography and used for calculating biomass production. Then, the respirometric activity and ergosterol production data were used to estimate biomass production with the program Fersol (F). The growth parameters resulted in an achieved specific growth velocity of 0.016 h-1 at 18 h and biomass yield (YX/O) = 0.160 g of biomass g-1 of consumed O2 at 302 h of fermentation. The analysis resulted in ergosterol values of 6.71 mg g-1 of fungi biomass (Dry Weight: DW) from submerged fermentation and 1.95 mg g-1 of solid-state-fermented wheat grains. The correlation with biomass production allowed us to estimate a value of 0.29 g g-1 of fungi biomass per gram of the solid-state-fermented wheat grains. The importance of this study is allow calculation of the fungi biomass percentage in solid-state-fermented wheat grains and determination of the growth parameters of the main mycelium A. brasiliensis in this substrate, which can be milled to obtain a bio-flour to produce nutraceutical foods with beneficial effects due the presence of ergosterol which has recognized antitumor activity.