[Objectives]  To examine whether the effects of the root-knot nematode, Meloidogyne incognita, infestation on Spodoptera litura larvae vary anoung different S. litura instars. [Methods]  S. litura larvae were randomly assigned to one of two treatment groups; one that was fed leaves of the Chinese tallow tree, Triadica sebifera, that were infested with M. incognita, and one that was fed nematode-free leaves, and differences in the growth (larval weight, development period, relative growth rate) and digestive ability (food intake, approximate digestibility, and food conversion rate) of these groups were measured and compared. [Results]  In general, food consumption and developmental period of S. litura gradually increased with larval development. Relative growth rate, larval weight, and food conversion rate first increased then decreased with larval development, whereas approximate digestibility first decreased, then increased, as larvae developed. The approximate digestibility of 2nd-instar larvae fed nematode infested leaves (0.78 ± 0.07) % was significantly higher (30%) than that of those fed nematode-free leaves. However, the larval weight (0.12 ± 0.04) g, relative growth rate (0.20 ± 0.06)   g·g^－1·d^－1, and food conversion rate (0.54 ± 0.18) % of 4th-instar larvae fed nematode infested leaves was significantly lower (61%, 36% and 73%, respectively), compared to larvae fed nematode-free leaves. There was no significant interaction effect between nematode infestation and instar on developmental duration or food consumption. [Conclusion]  Effects of root-knot nematode infestation on the growth and digestive ability of S. litura larvae varied with larval instar. Although nematode infestation significantly increased the approximate digestibility of 2nd-instar larvae, it greatly inhibited the growth and the digestive ability of 4th-instar larvae.