Detailed film cooling effectiveness distributions were experimentally obtained on a turbine blade platform within a five-blade linear cascade. A typical labyrinth-like seal was placed upstream of the cascade blades to simulate purge flow from a stator-rotor gap. Delta wings were periodically placed upstream of the blades to model the effect of the passage vortex generated in the vane passage on the downstream blade platform film cooling effectiveness. Typical vane passage vortex was simulated by two delta wings with height of 10% and 20% of the blade span, respectively. The strength of vane passage vortex was also modeled by varying the attack angle of mainstream to the delta wing. The film cooling effectiveness was measured with the delta wings placed at four phase locations, to investigate the effect of the passing vanes. The detailed film cooling effectiveness distributions on the platform were obtained using pressure sensitive paint (PSP) technique. The coolant mass flow rate varied from 0.25% to 1.0% of the mainstream flow. The freestream Reynolds number, based on the axial chord length and the exit velocity, was 750,000. The Mach numbers at the inlet and the exit were 0.27 and 0.44, respectively. The vortex generated by the delta wings had a profound impact on the platform film cooling effectiveness. The upstream vortex created more turbulent mixing within the blade passage and resulted in reduced film cooling effectiveness on the blade platform.