Many chemicals have the ability to attack on plastics as solvents and can lead to failure. In some cases, the source of the solvent is not well defined. In this study, the effect of biodiesel, a fatty acid methyl ester, on various plastics, namely polyamide 6 (PA 6), polycarbonate (PC), acrylonitrile-butadiene- styrene (ABS) and ABS/PC plastic blends was studied. Various feedstocks of biodiesel were also studied, including, soy bean oil (new and used), animal fat (tallow), corn oil as well as choice white grease. The plastics samples were tested under ASTM standard where a predefined strain is applied to the samples prior to exposure to the solvent (biodiesel). It was found that under the majority of combinations, other than PA 6, cracking was seen within 12 hours, and with ABS/PC and PC cracking was seen in minutes. Thus, it has been shown that biodiesel can be a degrading solvent for engineering plastics, such as PC, ABS and ABS/PC blends.