Unit commitment (UC) problem with ramp rate, for large number of units is a highly nonlinear optimization problem with huge number of constraints. This paper presents a new hybrid approach of 'Harmony Search (HS)' and 'Wavelet Mutation (WM)' algorithm (HS-WM) for UC problem. In this proposed hybrid HS-WM method, scheduling variables are handled in binary form and other constants are handled in decimal form. The efficiency of this method is tested on ten unit and hundred unit test system. Final results show that a minimum generation cost in less time interval, in comparison to the other existing results. © 2015 IEEE.