With the change of nutrient intake after the Second World War, obesity is becoming one of the most serious healthproblems in Japan. From a practical viewpoint for prevention of lifestyle related diseases, we planned an intervention trialof weight control for obese women. After obtaining informed consent, we recruited patients over 30 years old with a BMIof 24 or more for the present program. Forty patients were randomly assigned into study groups A (28) and B (12). GroupA started the prevention program at the entry and group B started three months thereafter, according to the protocol. Thistrial was designed to evaluate effectiveness of intervention trial during the first 3 months by comparing values with thosefor the non- intervention subjects. At the baseline and after three and six months, participants were checked for body size,dietary intake and serum chemistry. They were stressed to make a record not only of food intake but also physical activityover the 3 months. Every weekend they returned their record diaries by mail and we provided appropriate comments bytelephone and/or mail after reviewing them.After follow up for 3 months, we observed significant improvement in BMI, waist and hip size. There was a 4.2 %decrease of initial body weight on average after intervention but a 0.3 % increase in the group without intervention, thedifference between the two groups being statistically significant. With regard to change in key biomarkers in group A,decreased serum triglycerides appeared related to the reduction of BMI, but no link was apparent for total cholesterol.