In this retrospective longitudinal study, we focused on the clinical characteristics of Japanese individuals with recent onset impaired glucose tolerance (IGT) who have been followed up for insulin secretory function and 75-gram oral glucose tolerance test (OGTT) for more than 3 years annually before they progressed from normal glucose tolerance (NGT) to IGT. Subjects whose body weight did not show significant change for the period were selected and labeled as either NGT (no change in OGTT over 3 years) or IGT (progressors from NGT to IGT) groups (n = 24, each). We compared the basal biochemical data and response of plasma glucose and serum insulin after OGTT of the two groups. In the IGT progressors, significant increase of plasma glucose at 30 to 120 minutes during OGTT and significant decrease of HDL-cholesterol were observed since 3 years before onset of IGT. In addition to increase of serum glucose and decrease of HDL-cholesterol, serum insulin at 120 minutes during OGTT were significantly and remarkably high at onset and 3 years before onset of IGT. Plasma glucose at 30–120 minutes and serum insulin level at 120 minutes after glucose load are potentially significant predictors of progression from NGT to IGT even in subjects who do not show increase of body weight.