Though they are naturally anisotropic and heterogeneous, the mechanical behavior of masonry walls in the micro modeling for the purpose of nonlinear analysis, can be simplified by adopting the homogenization technique. In this, the Cartesian coordinates coincide with the bed joint and in perpendicular (in the direction of the head joint); then, the wall is treated as an orthotropic material. In this paper, the development of a ten parameters failure criterion is presented; where the parameters are obtained from experimental tests. The tests of Page are used to show how the procedure of regression analysis can be performed for a better prediction of the wall strength. The obtained results show the effectiveness of the homogenization technique and the reliability of the proposed regression procedure in the development of the failure surface. The proposed failure criterion allows the use of continuum damage mechanics and the incremental approach for tension and compression regimes by inserting damage variables to the criterion. The proposed failure surface and preliminary results show the potential of modeling masonry under biaxial state of stress.