Abstarct: Introduction: Obesity and overweight are significant contributors to the decline in quality of life and the development of various diseases in modern societies. To combat these issues, numerous strategies have been proposed, including engaging in physical activity in a fasted state and using supplements like caffeine, whose effects on enhancing mextabolism have been well-documented in recent years. Therefore, this study aimed to investigate the acute effects of caffeine consumption on fat and carbohydrate oxidation before, during, and after endurance exercise under fasted and fed conditions in overweight, untrained men. Materials and Methods: The study included 17 male students from Shahrood University of Technology with a mean age of 23.05 ± 4.95 years, a body mass index of 30.69 ± 4.25, lean body mass of 37.64 ± 3.70 kg, body fat percentage of 31.92 ± 7.15, and weight of 98.05 ± 12.58 kg. Participants provided informed consent and attended the physiology laboratory for four crossover sessions in fasted and fed states. During each session, a 10-minute baxseline respiratory gas analysis was conducted. Participants then consumed either 5 mg of caffeine per kilogram of body weight (encapsulated in cellulose capsules) or a placebo, followed by a 20-minute rest and re-measurement of respiratory gases. Subsequently, each participant performed 20 minutes of submaximal exercise at 60% Vo₂max, followed by a final 20-minute post-exercise respiratory gas analysis. Data normality was assessed using the Kolmogorov-Smirnov test, and ANOVA with Bonferroni post hoc tests was applied for statistical analysis at a significance level of P ≤ 0.05. Results: Significant differences in maximum carbohydrate oxidation were found between the (caffeine/fed) and (placebo/fasted) sessions (P = 0.045), as well as between the (caffeine/fed) and (placebo/fed) sessions (P = 0.050). Additionally, significant differences in maximum fat oxidation during exercise were observed between the (caffeine/fasted) and (placebo/fed) sessions (P = 0.007), and post-exercise maximum fat oxidation significantly differed between the (caffeine/fasted) and (placebo/fed) sessions (P = 0.001). Resting mextabolism post-exercise also significantly differed between the (caffeine/fed) and (placebo/fed) sessions (P = 0.001). No significant differences were observed for other comparisons. Conclusion: Acute caffeine supplementation appears to enhance carbohydrate oxidation before exercise and maximum fat oxidation during and after endurance exercise at 60% Vo₂max. It also increases resting mextabolism post-exercise but does not significantly influence energy expenditure during exercise