Background&Purpose: The aim of this study was to compare of maximal fat oxidation and the exercise intensity that elicit maximal fat oxidation (Fatmax) between active and inactive elderly men. Methodology: 10 healthy elderly men that had regular exercise (at least 10 past years, ,VO2max 44.6±4.5 ml.kg.min) and 10 healthy elderly men that hadn’t any regular exercise (at least 10 past years, VO2max 30.9±3.2 ml.kg.min), were selected as the subjects of this study. Then, the participants performed an incremental exercise test at 8 to 10 am in the fasting state, including: activity with 3 minutes stages on treadmill to exhaustion. The amount of maximal fat oxidation and Fatmax were measured through indirect calorimetry method using the gas analysis system with aim of stoichiometric equation. To compare the variables, independent t test (p>0.05) was used. Results: Fat oxidation rate in range of intensities, maximal fat oxidation and Fatmax in active elderly men was significantly higher than inactive elderly men (p<0/05). but, Carbohydrate oxidation rate in range of intensities were significantly lower in the active compared to inactive elderly (p<0/05). Conclusion: In general, it was found that better state of fitness in active elderly associated with more fat oxidation and less carbohydrate oxidation in range of intensities. Moreover the amount of maximal fat oxidation and Fatmax decrease in elderly, but This decrease can partly be prevented with regular exercise.