CONFINED MASONRY buildings are used in rural and urban areas of Iran. They performed almost satisfactory during past moderate earthquakes of Iran. There is not a methodology in Iranian Seismic Code (Standard 2800-3rd edition) to estimate their capacities quantitatively. In line with removing this constraint, an attempt is made to study in-plane behavior of two squared CONFINED MASONRY walls with and without opening by using a numerical approach. These walls are considered based on Iranian Seismic Code requirements. Finite element 2D models of the walls are developed and a pushover analysis is carried out. To model the non-linear behavior of the CONFINED MASONRY walls, the following criteria are used: (1) The Rankine-Hill yield criterion with low orthotropic factor to model the MASONRY panel; (2) The Rankine yield criterion to model reinforced concrete bond-beams and tie-columns; (3) The Coulomb friction criterion with tension cutoff mode to model the interface zone between the MASONRY panel and reinforced concrete members. For this purpose, the unknown parameters are determined by testing of MASONRY and concrete samples; and by finite element analysis. Comparing the results show that the initial stiffness, the maximum lateral strength and the ductility factor of walls with and without opening are different. Also, the severe compressed zones of the MASONRY panels within the confining elements are found different from what are reported for the MASONRY panels of infilled frames by other researchers. This study shows that a further investigation is needed for estimating capacity of CONFINED MASONRY walls with and without opening analytically and experimentally. Also where openings, with medium size are existed, the confining elements should be added around them. These issues can be considered in the next revisions of Iranian Seismic Code.