The present experiment has been conducted to investigate effects of a recirculation zone at a multi-slot film cooling system in a ramjet combustor. The tested model is a pre-diffuser typed ramjet combustor having a recirculation zone due to the large expansion duct. The recirculation zone directly affects on the film cooling effectiveness and heat transfer coefficient at the first two slots of multi-slot system. Results from experiments are divided into two flow regions - a recirculation region and a boundary layer developing region. In the former region, the film cooling effectiveness decreases rapidly due to the mixing effect by a shear layer between the recirculation flow and the injected coolant from the slot. In the later cases, the lip thickness to slot height ratio is a main factor on film cooling effectiveness due to the generated eddies behind the back step of slot lip. As the blowing rate increases, the film cooling effectiveness is enhanced for all cases due to the augmented momentum of injected coolant from the slot.