For honeycomb subjected to in-plane loading, there exist deformations in the height direction for cell walls due to effect of Poisson's ratio. Because these deformations are different for adjacent walls, the elastic modulus of honeycomb should be analyzed as a 3-dimensional problem. In this paper, the method of analysis for the equivalent elastic modulus proposed by authors in the previous report, in which the effect of height h of the honeycomb core on the elastic modulus is taken into account, is applied to theoretical formula for calculating Young's modulus E₁ and shear modulus G₁₂. Then, the validity of the proposed theoretical formula for elastic moduli E₁ andG₁₂ is verified comparing with the numerical results by FEM.