Spodoptera cosmioides Walker and Spodoptera eridania Stoll (both Lepidoptera: Noctuidae) are herbivorous insects affecting crop yield. Understanding midgut digestive enzyme properties in these caterpillars when feeding on different resources is important for control strategies of these agricultural pests. This study evaluated the activity of midgut digestive enzyme total proteases, trypsin, cysteine proteases, and chymotrypsin in S. cosmioides and S. eridania feeding on natural soybean and cotton leaves and artificial diets. The proteolytic activities of midgut digestive enzymes in S. cosmioides and S. eridania vary according to diet, suggesting adaptation of these caterpillars to different host plants in order to avoid the inhibitory effects of secondary metabolites through the overexpression of proteases. High activities occur for trypsin and total proteases in both insects indicating that these enzymes are potential targets for inhibition in pest control programs.