In this paper, a new metaheuristic technique based on genetic algorithm (GA), adaptive strategy and two constraint handling repair mechanisms is proposed for solving the Security Constrained Hydrothermal Unit Commitment (SCHTUC). The performance efficiency of the proposed technique is demonstrated on IEEE 30 BUS test system consisting of four thermal units and two hydro power plants. A wide range of thermal, hydraulic, and security constraints such as real power balance constraint, ramp rate, minimum up/down time, minimum and maximum limits of thermal and hydro units, prohibited operating zones (POZ), valve point effect, spinning reserve, available production, water dynamic balance and transmission line constraint are taken into account. The simulation results obtained from the new binary/real GA are compared with the outcomes obtained from some heuristic methods, such as DA-PSO and PSO-GWO to reveal the validity and verify the feasibility of the proposed technique. The test results show that the proposed metaheuristic technique has the capability of obtaining better solutions with respect to other optimization methods which are implemented on this optimization problem.