A new glyoxylate dehydrogenase which catalyzes dehydrogenation of glyoxylate to oxalate in the presence of cytochrome c has been purified as an electrophoretically homogeneous protein from the cell-free extracts of a wood-destroying basidiomycete Tyromyces palustris. The enzymatic reduction of cytochrome c was dependent on glyoxylate which was found to be the best substrate among the compounds tested. The Km value for glyoxylate was determined to be 2.7 mM at the optimal pH (8.0). The UV-visible spectra of the enzyme in oxidized and reduced forms indicate that the enzyme belongs to a family of flavohemoproteins. The flavin nucleotide isolated from the native enzyme by heat denaturation was identified as FMN. The enzyme (Mr 331000) consists of six identical homopolymers (Mr of subunit 59000), which were found to constitute a symmetric octahedral shape by electron-microscopic observation with a negative staining method.