Obesity Problem closed up recently in Tokyo made us carry out this survey on 6241 children aged 6 to 1.4 years, measuring height, weight and skinfold thickness. 1. Skinfold thickness has distinctly increased for these several years, specially at the center part of Tokyo. Extra-obese children above the 97 percentile distribution are estimated to have more than 30% of body fat corresponding to the body weight for male and more than 40% for female. Occurence rate of this extra-obesity was 7% at the center of Tokyo and 1% at the suburbs. Obese children above the 90 to 96 percentile are estimated to have about 20 to 30% of body fat for male and 30 to 40% for female. 2. Several estimation methods of obesity, using the indices W/H, W/H2, W/H3 and skinfold thickness are examined statistically. Even in case of the best index W/H2 which has the highest correlation with skinfold thickness, only 70% of the extra-obese children belonged to the some grades of both the index and skinfold thickness, and other 30% were incorresponding in both kinds of the grades. Consequently, any index derived from weight and height is not able to estimate obesity sufficiently.