An effective and economical method to enhance the electrode activity of metal oxide-graphene nano-composites has been developed using exfoliated clay nanosheets as an additive. The close similarities in 2D sheet-like morphologies and negative surface charges between exfoliated clay and graphene nanosheets make possible the homogeneous mixing of these two colloidal nanosheets. The crystal growth of Mn3O4 nanocrystals on the surface of negatively-charged clay/graphene nanosheets in the presence of ammonia yields Mn3O4-N-doped graphene-clay nanocomposites. The incorporation of rigid clay nanosheets is effective in decreasing the strong pi-pi interaction and severe aggregation of graphene nanosheets and in optimizing the porosity of the resulting nanocomposites. The clay-incorporated Mn3O4-N-doped graphene-clay nanocomposites show better electrode performance for lithium ion batteries than the clay-free homologue, underscoring the beneficial effect of clay addition on the electrochemical activity of Mn3O4-N-doped graphene nanocomposites. This is attributable to the improvement of charge transport properties and the optimization of pore structure upon the addition of clay nanosheets. The addition of clay nanosheets is also effective in improving the electrode performance of graphene-based nanocomposites for sodium ion batteries, confirming the universal usefulness of exfoliated clay nanosheets as an additive for exploring efficient electrode materials.