In the present work, flame spread over thin circular duct is investigated in normal gravity and microgravity environments at different opposed flow speeds varying from 10 cm/s to 30 cm/s. The microgravity experiments are performed using 2.5 s drop tower facility available at National Centre for Combustion Research and Development (NCCRD), IIT Madras. Simulations corresponding to experiments are carried out using 2D axisymmetric numerical model which accounts for char formation. The study shows that flame spread rate curves for circular duct with respect to flow speed in microgravity and normal gravity cross each other. At low flow speeds flame spread rate in normal gravity is higher than corresponding spread rate in microgravity and vice versa at high flow speeds. Formation of char downstream of flame over circular duct plays an important role in radiation heat feedback to inner surface of unburnt fuel which leads to the enhancement of the flame spread rate.