Corn stalks were converted to bio-oils by fast pyrolsis in an auger fed reactor at 400 and 450 degrees C. Both acid-pretreated and untreated corn stalks were pyrolyzed. Proximate and ultimate analyses of the corn stalk feeds and bio-oils were performed, and the bio-oils were characterized by gas chromatography/mass spectrometry (GC/MS), gel permeation chromatography (GPC), C-13 and H-1 NMR spectroscopy, pH, ash, and viscosity measurements, and solids content and water analyses. Corn stalks have lower lignin content than wood, leading to lower bio-oil yields, more water produced and different chemical compositions than pine wood bio-oil generated in the same auger reactor. Acid pretreatment of stalks increased the bio-oil yields and decreased the char yields at both pyrolysis temperatures. Acid-treated stalks had lower water content, and pH, viscosity, and filterable solid values were lower than those of bio-oil from untreated stalks. Several compounds found in the bio-oil from untreated stalks were not detected in the bio-oil from acid-treated stalks. Thirty two compounds were quantitated in the GC/MS analysis of the two bio-oils. Gel permeation chromatography analysis indicated the presence of a significant fraction of high boiling point compounds that did not pass through the GC columns with bio-oils from both pretreated and untreated stalks. Weight averaged molecular weights of 490 and 530 for acid-treated and untreated stalks, respectively, were indicated by GPC. Portable auger reactors might be used for local production of corn stalk bio-oils during harvest, thereby avoiding the need to transport bulky, low density corn stalk or stover biomass to biorefineries or power generation units.