In restructured power systems, independent system operators (ISOs) or regional transmission organizations (RTOs) execute the security-constrained unit commitment (SCUC) program to plan a secure and economical hourly generation schedule for the daily/weekly-ahead market. As the size of ISO/RTO increases, the current SCUC algorithms could face critical challenges ranging from modeling accuracy to calculation complexity. This paper introduces an efficient fast SCUC (F-SCUC) for large-scale power systems. Main components used in the proposed approach include single-hour unit commitment with network security, single-hour unit commitment adjustment, unit commitment, economic dispatch, and hourly network security check. A reasonable and operational strategy for fixing and unlocking the generating units is explored. The iterative SCUC solution is controlled efficiently to accelerate the execution. Finally, the quality of F-SCUC solution is improved by executing a quick MIP-based SCUC solution according to the F-SCUC results. A 1168-bus system Nvith 169 thermal units, a 4672-bus system with 676 thermal units, and two large systems with 1352 and 2704 thermal units are analyzed to exhibit the effectiveness of the proposed approach.