Economic load dispatch (ELD) problem is one of the basic and important optimization problems in a power system. However, considering practical constraints of real-world power systems such as ramp rate limits, prohibited operating zones, valve loading effects, multi-fuel options, spinning reserve and transmission system losses in ELD problem makes it a non-convex optimization problem, which is a challenging one and cannot be solved by traditional methods. Moreover, considering environmental issues, results in combined economic and emission load dispatch (CEELD) problem that is a multiobjective optimization model with two non-commensurable and contradictory objectives. In this paper, a modified harmony search algorithm (MHSA) proposed and applied to solve ELD and CEELD problem considering the abovementioned constraints. In the proposed MHSA, a new improvising method based on wavelet mutation together with a new memory consideration scheme based on the roulette wheel mechanism are proposed which improves the accuracy, convergence speed, and robustness of the classical HSA. Performance of the proposed algorithm is investigated by applying it to solve various test systems having non-convex solution spaces. To Show the effectiveness of the proposed method, obtained results compared with classical harmony search algorithm (HSA) and some of the most recently published papers in the area. (C) 2013 Elsevier Ltd. All rights reserved.