Abstract: Objective: To investigate the effect of a Transtheoretical Model (TTM) based and web-based lifestyle modification on weight-loss, dietary and exercise behaviors in people with prediabetes. Methods: A convenience sample of subjects with prediabetes was randomly assigned in intervention group (n=30) and control group (n=27). Intervention group received a 3-month web-based lifestyle modification and 3-month follow-up. The control group received the same 3-month intervention 3 months later. The outcome measures were weight loss, Food Frequency Questionnare 25 score and standardized activity measurement 3 and 6 months after intervention. Results: Subjects with prediabetes at each stage of follow-up in both group had a significant loss in physical components and modification in dietary and exercise behavior by analyzing intention-to-treat (P<0.05). There was a significant interaction for group assignment and physical components, dietary and exercise behavior after the 3-month intervention (P<0.05). Conclusion: TTM-based Internet interventionon behavior modification can effectively modify dietary and exercise behavior, reduces weight and blood sugar of people with prediabetes.