This study was performed to analyze the microbiological hazards of ready-to eat sandwiches and to evaluate the effect of implementing a hazard analysis and critical control points (HACCP) for quality improvement of ready-to-eat sandwiches. In total, 174 samples were examined for the microbiological hazard analysis. About 37.4% of the samples had an aerobic plate count ${geq}$6 log CFU/g, and the numbers of coliforms exceeded 3 log CFU/g in 82.2% of the samples. Additionally, Staphylococcus aureus, E. coli, and Salmonella spp. were detected in 10.3%, 4.6%, 1.1% of sandwiches, respectively. In contrast, E. coli O157:H7, and Listeria monocytogenes were not detected in any of the samples. The results of the microbiological verification after implementing a HACCP throughout the production process indicated that S. aureus, E. coli, Salmonella spp., E. coli O157:H7, and L. monocytogenes were not detected in any of the samples. Consequently, implementing a HACCP is effective for quality improvement of ready-to-eat sandwiches.