Symptoms of wood boring activity and Cerambycidae larvae in living oak trees (Quercus L. spp.) were discovered in October 2006 in the Sierra Fria, Aguascalientes, Mexico. Prompted by this finding, we conducted a field study to determine the wood borer species and its host preference and geographical distribution, and to record biological and ecological data. Adult specimens were obtained by caging infested bole samples in laboratory conditions as well as by installing screen emergence cages on infested trees in several locations in the Sierra Fria. Twenty-nine line transects were sampled in search of wood boring symptoms in living oak trees. Forty adult specimens were obtained during the 32-month study. Based on morphology and behavior, the insect was identified as Crioprosopus magnificus LeConte (Coleoptera: Cerambycidae), a new geographical record for this species. The main host for this insect is Quercus potosina Trel., but it also occasionally attacks Quercus grisea Liemb. and Quercus eduardii Trel. Wood boring symptoms attributed to C. magnificus were found along the Sierra Fria. Beetle emergence was confirmed in four locations. Observations on insect mating, longevity and oviposition are provided.