Land plants protect themselves from ultraviolet-B (UV-B) by accumulating UV-absorbing metabolites, which may also function as anti-insect toxins. Previous studies have shown that UV-B enhances the resistance of different plant species to pierce-sucking pests; however, whether and how UV-B influences plant defense against chewing caterpillars are not well understood. Here we show that UV-B treatment increased Spodoptera litura herbivory-induced jasmonic acid (JA) production in Arabidopsis and thereby Arabidopsis exhibited elevated resistance to S. litura. Using mutants impaired in the biosynthesis of JA and the defensive metabolites glucosinolates (GSs), we show that the UV-B-induced resistance to S. litura is dependent on the JA-regulated GSs and an unidentified anti-insect metabolite(s). Similarly, UV-B treatment also enhanced the levels of JA-isoleucine conjugate and defense-related secondary metabolites in tobacco, rice, and maize after these plants were treated with simulated herbivory of lepidopteran insects; consistently, these plants showed elevated resistance to insect larvae. Using transgenic plants impaired in JA biosynthesis or signaling, we further demonstrate that the UV-B-enhanced defense responses also require the JA pathway in tobacco and rice. Our findings reveal a likely conserved JA-dependent mechanism by which UV-B enhances plant defense against lepidopteran insects.