In utilization of small size red muscled fishes like mackerel, sardine, and filefish, mechanical dressing is usually required. The removal of dark muscle is also necessary to improve qualify of the product, which could hardly be done by mechanical process. As a method of separating dark muscle, specific gravity method using sugar solution was investigated in this study. And the effects of the level of specific gravity, the size and density of meat particles, and stability of meat particle float on the separation of dark muscle were discussed. From the results, effective specific gravity, in case of sucrose solution, ranged 1.067 to 1.072 for mackerel, 1.062 to 1.070 for sardine, and 1.072 to 1.077 for filefish, respectively. The maximum separation of more than $90\%$ was obtained at specific gravity of 1.075, 1.070, and 1.075 in cases of mackerel, sardine and filefish, respectively. The size of meat particles which were ground with 0.2cm orifice plate was adequate to yield $90\%$ separation or above. The meat particle float in the glucose solution began to precipitate within 5 minutes after separation while 25 minutes in case of sucrose solution. Lipids were also fairly removed by the dark muscle separation process.