Previous studies demonstrated that lifestyle modification can prevent type 2 diabetes mellitus (T2DM) among those with impaired glucose tolerance, but similar beneficial results have not been proven among those with impaired fasting glucose (IFG). This randomized controlled trial investigated the efficacy of 3-year individual-based lifestyle intervention on T2DM incidence in the overweight Japanese with IFG. The adjusted hazard ratio in the frequent intervention group was 0.56 (95% confidence interval [CI], 0.36-0.87). In the post hoc subgroup analyses, the hazard ratio decreased to 0.41 (95% CI, 0.24-0.69) among those with impaired glucose tolerance at baseline, and to 0.24 (95% CI, 0.12-0.48) among those with a baseline hemoglobin A1c (HbA1c) level of 5.6% or more (Japan Diabetes Society method). Lifestyle modifications could prevent T2DM among those with IFG. In addition, identifying individuals with more deteriorated glycemic status by using HbA1c or 75-g oral glucose tolerance test, especially HbA1c, could enhance the efficacy.