Abstract
We investigate the mass difference between the π and η mesons by using lattice QCD with the Wilson fermion formulation. The calculation of the effective potential is done by the 1/N expansion in the strong-coupling limit. From a tree-level analysis of the effective potential we obtain the result that there is no mass difference in the parity-conserving phase to all orders in the 1/N expansion and that there exists a mass difference in the parity-violating phase.