Abstract: Many animals adopt intermittent gaits (burst-and-coast or flapping-and-gliding) during flying or swimming. We compare the performances of self-propelled foils driven by intermittent and continuous pitching motions, and attempt to answer the question whether the intermittent gaits are more efficient. Numerical simulations are conducted by solving the Navier-Stokes equations together with the dynamics equations of the foil. We study cases of continuous pitching at various frequencies and also cases of intermittent pitching at a fixed frequency but different duty cycles. The results indicate that, for a given cruising speed, the continuous gait is more efficient at lower speed, while the intermittent gait is more efficient at higher speed. The different flow structures produced by the continuous and intermittent gaits are presented. The results obtained in this work can benefit the design of efficient bio-inspired underwater vehicles.