Species of Leptographium are well-known inhabitants of conifers in the Northern Hemisphere, in which they cause a blue-stain. They are also known to be associated with insects, especially bark beetles (Coleoptera: Scolytidae). Surveys of dying stands of Siberian fir (Abies sibirica) have resulted in the consistent isolation of an unknown Leptographium from the galleries of the fir sawyer beetle, Monochamus urussovi (Coleoptera: Cerambycidae). This fungus is responsible for the blue-stain in living trees. Comparison with known species of Leptographium led to the conclusion that it had not been previously described, and the name Leptographium sibiricum sp. nov. is introduced here.