The transient effect of unsteady wakes on film cooling effectiveness using a fast response pressure sensitive paint (PSP) was studied. Testing was performed in a five-passage, low-speed wind tunnel using a scaled-up high pressure, blade profile. The blowing ratios studied include 0.4, 0.8, and 1.2 with a density ratio of 1.0 and 1.5 at each blowing ratio. An upstream wake generator produced Strouhal numbers of 0.1 and 0.3 while the wind tunnel inlet mainstream Reynolds number was held at a constant value of 300,000 for every test case. The results in this paper confirm the overall time averaged reduction in film cooling effectiveness with the addition of an unsteady wake while providing more detailed information on the transient response of the film cooling effectiveness, presented in the form of film cooling effectiveness RMS values. Results show that film cooling effectiveness RMS values increase on the leading-edge region of the blade and show little change on the pressure side of the blade with an increase in the Strouhal number. On the suction side, the area-averaged effectiveness RMS values decrease for the 0.8 and 1.2 blowing ratios and remain unchanged for the 0.4 blowing ratio. A change in the density ratio of the coolant from 1.0 to 1.5 has a minimal effect on area-averaged effectiveness RMS values for all areas of the blade.