This paper presents a modelling approach for estimating seismic behavior of rocking masonry walls with unbonded post-tensioning. The proposed modelling approach estimates the rocking motions of these walls including the inelastic deformations in the masonry at the wall toes and associated continuous energy dissipation in the forms of viscous damping and hysteresis action. Following previous research, which shows that these walls can experience small flexural deformations in addition to rocking, an elastic flexural mode is also included. Accordingly, a system of nonlinear equations is developed and impulse-momentum equations are employed to estimate the impact energy losses in the walls. The proposed modelling approach is compared against past experiments of a rocking masonry wall with unbonded post-tensioning, which was subjected to a series of shake table motions. Modelling results show good agreement with the experimental responses, including displacement time histories, variations in post-tensioning forces and neutral axis depths, and force-displacement behavior.