This paper reports on some experimental investigations on ductility of reinforced concrete beams in flexure and evaluation of size effect. The minimum flexural reinforcement has been evaluated from experimental observations on ductility of reinforced concrete (RC) beams. Beams of depth 100 mm, 200 mm, 400 mm at different flexural reinforcements namely 0.15,0.30,0.60 and 1.0% were tested under uniform bending moment. The beams were made of 30 MPa concrete. The cracking and ultimate flexural strength, influence of beam depth on ductility and rotation capacity have been analyzed. The size of RC members has a significant influence on flexural behaviour. The variation of cracking strength is not very conclusive in small-size beams, where as it decreases as depth of beam increases beyond 200 mm. The ultimate flexural strength has been observed to decrease as the beam size increases. As the flexural reinforcement ratio in beams increased the ductility of beams was observed to increase. Ductility of RC members decreases with increase of beam size. The optimum flexural reinforcement has been obtained from an optimum ductility number, Np, equal to 0.20. The minimum flexural reinforcement was observed to decrease as the beam depth increased, and decreased as the yield strength of steel reinforcement increased. © 2007 Taylor & Francis Group.