An experimental investigation has been performed to study the film cooling of a smooth expansion exit at the leading edge of a gas turbine vane. A two-dimensional cascade has been employed to measure the cooling performance of the proposed expansion using a transient Thermochromatic Liquid Crystal technique. One row of cylindrical holes, located on the stagnation line, is investigated with two expansion levels at the hole exit, 2d and 4d, in addition to the standard cylindrical exit. The air is injected at 0 and 30 inclination angles with the mainstream direction at four blowing ratios ranging from 1 and 2 and a 0.9 density ratio. The Mach number and the Reynolds number based on the cascade exit velocity and the axial chord are 0.23 and 1.4E5, respectively. The detailed local cooling effectiveness over both the pressure side and the suction side are presented in addition to the lateral-averaged cooling effectiveness. The proposed expansion enhances the coolant distribution over the leading edge, particularly over the suction side. The cooling effectiveness increases with the increase of the blowing ratio due to the decrease in the jet lift-off, hence higher cooling capacity is provided. The complete confrontation between both streams on the 0 inclination angle causes a strong dispersion to the coolant, yielding a significant reduction in the effectiveness.