Summary: In this article, we shall deal with the existence theory for a self-adjoint coupled system of three nonlinear second-order ordinary differential inclusions with cyclic anti-periodic boundary conditions on an arbitrary domain. We consider convex valued as well as non-convex valued right-hand side of the given system and apply the standard fixed-point theorems for multivalued maps to drive the desired existence results. Finally, we give examples for the illustration of the obtained results.