This study evaluates the change in particle size of dry-milling corn ethanol co-products by using ultrasonic energy to increase the production of the biogas from the anaerobic digestion of ethanol dry-milling co-products, namely: dried distiller grain with solubles (DDGS), solids, thin stillage, and corn-syrup. The co-product samples were treated with various ultrasonic conditions and compared to non-treated samples (control sample). The ultrasonic amplitude was varied from 52.8 µm pp to 160 µm pp and the sonication time was varied from 10 to 50s. The samples were characterized with scanning electron and optical microscopy (SEM, OM) and particle distribution analysis (PDA). It was found that with solid/liquid suspensions (DDGS, solids), there was a significant decrease in particle size, increasing the surface area to volume ratio, to possibly enhance biogas yield during anaerobic digestion of these materials. In the case of thin stillage and corn syrup, the results were surprising in that an increase in particle size was seen.