Two pot experiments and a field study were conducted in a Randomized Complete Block Design (RCBD). The experiments were conducted to determine the effect of Glomus mosseae, a mycorrhiza fungus, on the reaction of four improved cowpea varieties to Meloidogyne incognita. Cowpea plants were inoculated with a single or a combination of5 000 eggs of M. incognita and 50 g of G. mosseae inoculum containing 5 spores/g of soil. The standardized method of screening and reporting resistance of crop germplasm to root-knot nematodes at 60 days after planting, and the modified version of including yield for resistance rating at harvest were used for this study. Root galling due to M. incognita infection was significantly lower on all the cowpea varieties treated with G.mosseae and more significantly on IT90K-277-2 and IT89KD-288 in the screenhouse. G. mosseae, suppressed root-knot nematode reproduction on all the varieties compared to cowpea plants infected only by M. incognita both in the screenhouse and field experiments. Also, G. mosseae mitigated the damage attributable to the root-knot nematode on all these varieties. Using Gall Index (GI), reproduction factor and yield, G. mosseae was effective in improving the resistance of the cowpea varieties to M.incognita. IT90K-76 cowpea variety was consistently resistant to the root-knot nematode, while IT90K-277-2 was tolerant with M. incognita infection but resistant with G. mosseae treatment. IT90K-941-1 variety was resistant in the screenhouse. The results of this study also confirmed G.mosseae as a potential bio-control agent for M. incognita on these cowpea varieties.