The hydrodynamics of a flexible foil, which is inspired by the thunniform kind of propulsion system, is studied numerically. The NACA0012 foil with a chord length of 0.1m is selected for the study. The foil performance parameters such as force coefficients and efficiency are estimated for different flexibility of the foil and Strouhal numbers. The results show that oscillating foil generated thrust increases with increase in Strouhal number up to 0.4 and a maximum efficiency is achieved at St=0.15. © Copyright 2017 ASME.