Vortex tube is the device that can separate small particles from the compressed gas, as well as compressed gas into hot and cold flow. Because a vortex tube uses strong swirl velocity, it generates a high pitch noise. In this study 4 different silencers are tested to reduce vortex tube flow noise. Three are commercial silencer applied in pneumatic system, and the other is perforated silencer. As a result, 1/4 inch silencer shows the best sound absorption characteristics for all inlet air pressure range. 1/2 inch and 3/8 inch silencer show very similar sound absorption characteristics. However, perforated silencer shows sound absorption characteristics similar to 1/2 inch silencer at low inlet pressure, but shows the worst characteristics at high inlet pressure.