The aim of research was to study the factors affecting quality of reduced sodium steamed mackerel during chilled storage. This study varied the concentration of sodium chloride (NaCl) (20, 15, 10, 5 and 0%) combined with the concentration of potassium chloride (KCl) (20, 15, 10, 5 and 0%), cooking time (1, 3, 5, 7 and 9 min). The proper reduced sodium steamed mackerel were tested by using different types of packaging (polystyrene and polyvinyl chloride; PVC and PS), Linear Low Density Polyethylene (LLDPE) and Nylon Linear Low Density Polyethylene (NLLDPE). All samples were kept refrigerated at 4±2°C for 7 days. The experimental design was used response surface methodology (RSM). Results showed that the proper reduced sodium steamed mackerel used 10% NaCl combined with 10% KCl and steamed for 3 min had the sodium and potassium values of 5,817 และ 5,997 mg/kg and received highest overall sensory score (8.40). The values of the sensory score were no significant difference from the control (30% NaCl) (8.25) (p>0.05). The shelf life of reduced sodium steamed mackerel packed in PS and PVC was only 3 days having total microbial count higher than the standard. While, the reduced sodium steamed mackerel packed in LLDPE and NLLDPE had the shelf life of 6 days at 4±2°C. The microbiological result of total plate count was not exceeding the standard. No E. coli, Salmonella spp. yeast and mold were detected.