The purpose of this study was to evaluate the effect of various exercise intensity on Excess post exercise energy expenditure (EPEE), Resting Metabolic Rate (RMR),thyroid hormonal changes and biochemical variables in obese and NIDDM patients. The subject of the present study were divided into four groups and four periods: trained (T; n=10), control (C; n=10), obese (O; n=10) and NIDDM (N; n=10) group. And the periods were divided as follows; Resting (RE), Maximal (MA), High intensity (HI), and Low intensity (LI). There was significant difference in RMR among different intensity of exercise. in the T (p<0.05) not in the C, O, and N groups. however, there was no significant different percent body fat among all groups. In the energy expenditure, there was significant different among C, O, N groups compare to T in HIEE (high intensity exercise energy expenditure), LIEE (low intensity exercise energy expenditure), HIEEPE (high intensity exercise energy expenditure post exercise) and LIEEPE (low intensity exercise expenditure post exercise). In the hormonal level, there was significant different in T4 level in the T group at LI period and there was also significant difference in T4, Free T3, & Free T4 levels in T group at LI period, however there was no significant different in the O and N groups except LI period. In the fatigue variables, there was significant different in lactate and ammonia levels in the N group in the period of HI compare to C. The present cross-sectional study was design to investigate the relationship between exercise intensity and RMR in four groups. The focus of this investigation was to compare RMR in aerobically trained (T), control (C), obese (O) and NIDDM (N) group. The relationship among RMR, exercise intensity and percent body fat would best be investigated using Meta Lyzer 3B, MMX3B and body composition analyzer. Each subject completed measurement of percent body fat, RMR, hormone in the period of maximal oxygen uptake exercise (MA), high intensity exercise (HI), and low intensity exercise (LI). From the results, High and Low intensity of exercise, there was a trend for an increased RMR (kcal/day) in the trained groups and control group (in case of LI) not for the obese and N groups. This is best explained not by the reduced percent body fat but by the highly induced energy expenditure (during exercise and post exercise energy expenditure) and increased T4, Free T3, and Free T4 hormonal levels in the low intensity exercise for the T group and sometimes C group.