It is well known that obesity can negatively affect health and function which may be partly restored by several aerobic exercise programmes. We quantitatively investigated the effect of aerobic exercise on the cardiopulmonary fitness in obese Thai women (BMI 29.41 ± 2.9 kg/m2, aged 45 ± 5.34 yrs). The aerobic exercise training (AET) consisted of 12 weeks of leg cycling on an electronically controlled cycle ergometer at or near anaerobic threshold (AT) (30 min/session, 3 sessions/week, 12 weeks). Peak oxygen uptake (VO2peak) and 6 minute walk test (^MWT) were used as a measure of cardiopulmonary fitness. Values are means ± SD. The AET resulted in significant reductions in body mass 2.5 kg (p<0.01), BMI 1.0 kg/m2 (p<0.01), waist circumference 4.1 cm (p<0.05), hip circumference 3.2 cm (p<0.05), % body fat 2.98% (p<0.001), FM 2.95 kg, (p<0.001), SBP 10.9 mmHg (p<0.01), DBP 8.8 mmHg (p<0.01) and MAP 9.5 mmHg (p<0.01) but not FFM. Additionally, it increased VO2peak by 21.6% (p<0.01), work load at anaerobic threshold by 14.3% (p<0.01), maximal work load by 10.7% (p<0.01) and 6MWT by 14.3% (p<0.01) compared to pre- exercise. These data suggest that a 12-week exercise training programme increased cardiopulmonary fitness, aerobic capacity and physical performance but reduced body weight, body composition, SBP, DBP and MAP in obese women.