In recent decades, xylanases have been used in many processing industries. This study describes the xylanase production byPenicillium glabrumusing brewer's spent grain as substrate. Additionally, this is the first work that reports the purification and characterization of a xylanase using this agroindustrial waste. Optimal production was obtained whenP. glabrumwas grown in liquid medium in pH 5.5, at 25 °C, under stationary condition for six days. The xylanase fromP. glabrumwas purified to homogeneity by a rapid and inexpensive procedure, using ammonium sulfate fractionation and molecular exclusion chromatography. SDS-PAGE analysis revealed one band with estimated molecular mass of 18.36 kDa. The optimum activity was observed at 60 °C, in pH 3.0. The enzyme was very stable at 50 °C, and high pH stability was verified from pH 2.5 to 5.0. The ion Mn²⁺and the reducing agentsβ-mercaptoethanol and DTT enhanced xylanase activity, while the ions Hg²⁺, Zn²⁺, and Cu²⁺as well as the detergent SDS were strong inhibitors of the enzyme. The use of brewer's spent grain as substrate for xylanase production cannot only add value and decrease the amount of this waste but also reduce the xylanase production cost.