The effect of base roughness on the seismic behaviour of roller compacted concrete gravity dams were investigated by pseudo-dynamically testing two 1/75 scaled specimens with smooth and rough base treatments. Both specimens were tested under the effect of three different hazard level earthquakes and also a pushover experiment was conducted to obtain the capacity curve of each specimen. The smooth base specimen exhibited significant sliding under the effect of the maximum credible earthquake motion. In contrast, the rough base specimen had no base sliding response even during the pushover experiment, whereas large body cracks reaching almost the downstream toe of the specimen was the main reason for the loss of lateral strength. The numerical simulation of these two experiments were also conducted by using the sliding response analysis and the finite element method. The base sliding response of the smooth-base specimen was simulated successfully by considering a variable friction coefficient. The finite element results for the rough-base specimen was also promising as far as the base shear and tip displacement estimations were considered. However, the crack propagation estimates were inconclusive due to the severe diffusion of the cracks.