Abstract: Two strains of the fungus Aspergillus niger were screened for their ability to produce citric acid on corn distillers` dried grains with solubles. It was determined that citric acid production by A. niger ATCC 9029 after 240 h was higher on untreated grains than on autoclaved grains or acid-hydrolyzed grains. In contrast, citric acid production by A. niger ATCC 12846 after 240 h was higher on autoclaved grains than on untreated grains or acid-hydrolyzed grains. Methanol or phosphate supplementation to the grains failed to stimulate citric acid production by either A. niger strain. Biomass production by both strains after 240 h was higher on the treated grains than the untreated grains. The highest citric acid yields were observed following growth of both strains on the untreated grains.