In this study, we propose a method for estimating the anisotropic material properties of glass fiber reinforced plastic (GFRP) from the in-plane elastic modulus. The anisotropic material properties have to be determined and taken into consideration in order to predict the GFRP deformation using the finite element method (FEM). We used a homogenization method to calculate the anisotropic material properties. To do this, the material properties of the glass fiber and resin have to be input. However, the material properties of the resin are sometimes unknown, due to changes in the material properties resulting from variations in the manufacturing conditions. We predicted the anisotropic material properties of the GFRP in this study by inputting the in-plane material properties of the GFRP to the response surface. We applied this method to the GFRP for a printed circuit board, and calculated the anisotropic material properties without any resin material properties.