In this study, it is the first time that the effect of slip on the entropy generation is investigated for the flow over a rotating single free disk. The problem is considered for steady and axially symmetrical case in a Newtonian ambient fluid. The classical approach introduced by Von Karman is followed to reduce nonlinear flow and heat field equations to ordinary differential equations. Then these equations are solved by using differential transform method. Entropy generation equation for this system is then derived and nondimensionalized. This equation, which has never been introduced for such a geometry and boundary conditions before in open literature, is interpreted for various physical cases by using nondimensional parameters of fluid and heat fields. It is observed that the effects of slip are to reduce the magnitude of entropy generation and to reduce the total energy in the system by reducing velocities and velocity gradients. Also, while entropy generation reduces, Bejan number converges to 1 with increasing slip factor.