Secondary flows in airfoil passages have become increasingly important in the design of modern gas turbines as a result of several fundamental trends in gas turbine engine development. Driven to achieve higher engine efficiencies and specific thrust output, the gas turbine industry is continually pushing the envelope of maximum allowable turbine inlet temperature. Whereas many researchers have worked to gain an understanding of secondary flows and their effects on turbine heat transfer, very few have pursued ways to mitigate passively their detrimental effects. Although considerable attention has been given to techniques of secondary flow reduction to minimize the associated aerodynamic losses, improvement of the thermal environment for a turbine vane is sought. In particular, this objective is achieved through optimizing a fillet in the vane‐endwall junction to minimize adiabatic wall temperatures. The approach taken is to employ a commercial optimization software package in conjunction with a computational fluid dynamics package in the design of the fillet. Results indicate that significant reductions in adiabatic wall temperature can be achieved through application of an optimized fillet.