Oscillating water columns (OWC) are widely used devices for the extraction of wave energy through self -rectifying impulse air turbines. To improve the performance of any turbo-machinery, guide vanes (GV) play an essential role in deciding turbine characteristics in terms of efficiency and torque. The concept of filleting is used in the GVs of bidirectional impulse turbine (BDI) with five different types of GV fillets for different radii, and the performance was analyzed. The numerical simulation was done using the commercial code ANSYS CFX 16.2, which solves the three-dimensional Reynolds-Averaged Navier-Stokes equation by finite volume explicit Runge-Kutta scheme with the k-ω SST closure model. There is a close agreement between the experimental and the numerical model. The detailed flow physics of filleted GVs have been included in the present work, and it was found that the efficiency increases at higher flow coefficients.