In this study, we aimed to evaluate the nematicidal activity of cinnamon bark extracts (CE) and chitosan (Cs) against Meloidogyne incognita under in vitro, pot, and field conditions. In the pot experiments, CE mixed with Cs effectively inhibited M. incognita infection on black pepper plants. We applied the following formulations, which all significantly reduced the gall index and nematode number in 5 g of root and 100 g of soil: CE:Cs = 5 mg:20 mg, 10 mg:40 mg, and 15 mg:60 mg per pot. In addition, the application of CE:Cs = 32 mg:120 mg, 64 mg:240 mg, and 96 mg:360 mg per plant effectively reduced root gall formation and nematode density in black pepper roots and soil compared with that of the non-treated control under field conditions. Nematode density in the black pepper roots was positively correlated with the percentage of plants with yellow leaves. These results suggest that cinnamon mixed with chitosan may be used as an effective and eco-friendly pesticide against plant parasitic nematodes.