Specimens of horse mackerel were killed by stabbing in the spinal bulb or neck-breaking. After death, the fishes were stored at 0°C. The rate of progress of rigor-mortis, and the rate of change of concentrations of energy-related compounds and breaking strength of the dorsal muscle were investigated. The rate of progress of rigor-mortis in the neck-breaking group was slower than that in the stabbing in the spinal bulb group. The concentrations of ATP and creatine phosphate in the dorsal muscle immediately after killing in the neck-breaking group were higher than those in the stabbing in the spinal bulb group. Conversely, the initial values of concentrations of IMP and lactic acid were lower in the neck-breaking group. No significant differences were observed in the changing rates of breaking strength of the muscle and K-value. From these results, it was considered that the killing procedure by neck-breaking was able to delay the changes in rates of rigor-mortis and energy-related compounds in muscle compared with the treatment by stabbing in the spinal bulb.