A rotational motion model for a serpentine belt drive system was devel oped in which the belt damping and the effect of the belt deflection along conta ct arc of the pulley on the tension were considered. The rotational motion model was solved numerically. The slip factors were used to predict the onset of belt slipping on the pulleys. The effects of the belt damping on the vibration chara cteristics and the belt slipping were studied. Control of belt slip on pulleys b y adjusting the preload of the tension spring and the installed position of the tensioner arm was analyzed. The rotational motion model of the serpentine belt d rive system and the numerical methods solving the model presented in this paper were useful to the design of the belt drive system. The results provided some in structions in controlling the belt slipping on the pulleys.