An important parameter that is being not accounted for in the design of concrete structures is the size of structure on strength. Size effect in shear has been a serious concern owing to sudden failure of large size members at lower stress levels compared to small size members. Currently, the design provisions for shear in reinforced concrete (RC) members by various codes of practice have not accounted for the size effect. In this paper some experimental investigations have been carried out in order to study the size effect on RC beams with a shear span-to-depth ratio 1.05. Geometrically similar beams were tested by varying depth of member and compressive strength of concrete under four-point loading. The shear reinforcement was varied maintaining balanced flexural reinforcement in all the beams. Sudden failures of beams have been observed in larger size beams cast from high strength concrete (HSC), which exhibited a strong size effect on strength. The observations from the study reveal that the effect of size of beam on shear strength in the design of large size RC members should be incorporated.