Plants damaged by herbivorous insects often respond by mounting a series of defense responses that can inhibit the insect's fitness. Ostrinia furnacalis (Guenée) (Lepidoptera: Crambidae) is a major insect pest in maize throughout much of Asia, Australia, and the western Pacific islands. We examined the effects of O. furnacalis-induced maize defenses on O. furnacalis fitness, and explained the effects from biochemical changes that occur in maize leaves in response to O. furnacalis feeding. The results of the age-stage, two-sex life table showed that significantly longer larval and pupal life spans, and total preoviposition period (TPOP) occurred. A decrease in the longevity and fecundity of female adults was observed in O. furnacalis fed on O. furnacalis-damaged leaves. The mean generation time (T), finite rate of increase (λ), net reproductive rate (R₀), and intrinsic rate of increase (r) were also correspondingly affected. Biochemical assays indicated that 24 h of O. furnacalis herbivory resulted in decreased levels of the benzoxazinoids, 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), and 2-(2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one)-β-D-glucopyranose (DIMBOA-Glc), and a corresponding increase in 2-(2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one)-β-D-glucopyranose (HDMBOA-Glc). Maize also exhibited higher activities of the defensive enzymes—peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), and polyphenol oxidase (PPO)—after 24 h of herbivory. We concluded that exposure to O. furnacalis-damaged leaves had an inhibitory impact on the fitness of the neonate to pupa stages of O. furnacalis. The observed higher level of HDMBOA-Glc and higher enzymatic activities of POD, SOD, CAT, and PPO may account, in part, for the observed inhibitory effects on O. furnacalis fitness.