(Nd_1−xLa_x)NbO₄ ceramics were prepared via a conventional solid-state reaction route and the correlations among bond ionicity, lattice energy, phase stability and microwave dielectric properties were investigated. The diffraction patterns showed that the (Nd_1−xLa_x)NbO₄ ceramics possessed a monoclinic fergusonite structure. The chemical bond ionicity, bond covalency and lattice energy were calculated using the empirical method. The phase structure stability varied with the lattice energy which resulted due to the substitution content of La³⁺ ions. With the increase of La³⁺ ion contents, the decrease of Nd/La–O bond ionicity was observed, which could be attributed to the electric polarization. ε_r has a close relationship with the Nd/La–O bond covalency. The increase of the Q × f values and τ_f values could be attributed to the change in the lattice energy. The microwave dielectric properties of (Nd_1−xLa_x)NbO₄ ceramics with a monoclinic fergusonite structure were strongly dependent on the chemical bond ionicity, bond covalency and lattice energy.