Ground beetles (Coleoptera: Carabidae) are important components of soil ecosystems in temperate zones, but our knowledge regarding the ecology of many species is limited. This study examined larval food habits in the ground beetle Amara (Curtonotus) gigantea (Motschulsky) using laboratory-rearing experiments. Because this beetle is a member of the tribe Zabrini, which includes several species that exhibit granivory during larval and/or adult stages, three diet types were tested, with starvation as a control: Tenebrio larvae, mixed seeds (Bidens pilosa (Asteraceae), Setaria spp., Digitaria ciliaris (both Poaceae), and Humulus scandens (Moraceae)), and Tenebrio larvae + mixed seeds. Because of high larval mortality during overwintering under laboratory-rearing conditions, survival and the duration of development through pre-overwintering stages (first and second instars) were compared. Larvae fed the diet of Tenebrio larvae + mixed seeds showed the highest survival (89%), followed by the diet of Tenebrio larvae (83%), but the difference between the two treatments was not significant; similarly, developmental durations did not differ between these two diets. Larvae fed the mixed-seeds diet showed markedly lower survival, and no larvae reached the second instar. Therefore, for A. gigantea larvae, animal food results in high larval performance, whereas seeds provide a low value diet; animal food is essential for larval development, but seeds provide no benefit, even as a dietary supplement. Overall, the present results suggest that A. gigantea larvae are omnivorous but with a mainly carnivorous food habit.