The blockage of the cooling jet hole is one of the problems that arises in the film cooling of gas turbines. It reduces the film cooling effectiveness and creates hot spots. In this research, by following the pattern of blockages created in the used turbine blades of G17-79 engines and after constructing its nearly cylindrical hole model, the required tests were conducted using a wind tunnel to investigate the effects of blockage. The desired tests were performed at four blowing ratios of 0.4, 0.5, 0.7, and 0.8 at the free stream Reynolds number of 10000, based on the jet hole diameter . Thermal data acquisition was performed using infrared camera and the obtained results show that the cooling effectiveness decreases, in comparison to the holes which have no blockages. This reduction, is due to higher interaction of the jet flow with the cross flow which is due to increase of jet velocity at the jet exit. Also, by increasing the blowing ratio, the film cooling effectiveness decreases. However, at the blow ratio of 0.4, the highest effectiveness all over the investigate domain was observed.