This paper presents Grey Wolf Optimization (GWO) Algorithm in order to solve Short-term Hydro-Thermal Scheduling (SHTS) problems. With large number of variables the non-linearity of the search space of SHTS problem increases and most algorithms are not capable to give enough diversity in the crowds of swarms for finding better solutions. However, the unique characteristic of GWO algorithm increases the diversity in solutions and the search capability. The performance of the proposed algorithm is experimented on two short term multi reservoir cascaded hydrothermal systems. First test case is moderately large while the second test case is a considerably large one. Experimental results demonstrate the superior performance of the proposed algorithm as compared to other recently reported ones in terms of convergence and better quality of solutions.