XY positioning is an important task in industrial applications. This paper addresses the dynamic modeling of a belt-driven, parallel-type XY positioning system constructed in the form of a capitalized H. The system uses one long timing belt to transmit the rotation of two stationary motors to end-effector motion. Due to less moved masses, the studied H-frame system is potentially capable of fast acceleration, and therefore, faster positioning than traditional stacked systems. The use of an elastic transmission element also causes the biggest disadvantage of the system, which is an uncertainty of end-effector position due to stretching in the belt. Thus, the objective of this paper is to develop a dynamic model that can capture the response of this system. Using Lagrange's method, an eighth-order lumped parameter dynamic model of the stage motion is derived. The effect of nonlinear friction in the pulleys and cart motion is added to the model. The response of the model was simulated in MATLAB Simulink, and the model prediction is compared with real data obtained from the developed system. The results show that the model can accurately predict the dynamics of the developed H-frame positioning system.