This study was performed to investigate the interrelationship between fasting serum insulin, eating behaviour, daily energy intake and the fatness in obese and non-obese women. The possibility of fasting serum insulin as potential predictive factor for eating behaviour and daily energy intake was also investigated. The results are as follows: 1) In obese women ; Subjects with higher fasting serum insulin were associated with higher speed of eating and shorter meal duration time. No association could be found between daily energy intake or the degree of obesity and fasting serum insulin. There was a significant positive correlation between obesity, daily energy intake and speed of eating. Obesity, daily energy intake were negatively related to meal duration time. Subjects with a rapid speed of eating were apt to overeat during eating behaviour experiment. Our findings suggested that a rapid speed of eating is a contributing factor to the development of obesity in obese women. 2) In non-obese women ; While subjects with higher insulin level were apt to overeat, we could not find any relation between overeating and daily energy intake. There was no correlation between eating speed and daily energy intake, but a significant positive correlation was found between meal duration time and daily energy intake. The degree of fatness was increased with the lower daily energy expenditure per body weight, or the higher waist hip girth ratio, fasting serum insulin and daily energy intake.