In this experimental study, performances of counter flow type Ranque-Hilsch vortex tubes (RHVT), with a length to diameter ratio (L/D) of 12-16, were investigated for aluminum whereby the internal diameter (D) of RHVT was 9 mm. Flow was controlled by a valve on the hot outlet side, where the valve was changed from a nearly closed position to its nearly open position. Exergy measures the usefulwork obtainained from the energy source or material, and is based on the chemical energy embodied in the material or energy based on its physical organization relative to a reference state. Exergy analysis of RHVT of various length to diameter ratios (=12-16) and fraction of cold flow (ksi) = 0.1-0.9 were determined under 400 kPa pressurized air. The experimental system was modeled as a thermodynamic open system. As a new approach, this study proposes determination of the exergy efficiency by using Rule-Based Mamdani-Type Fuzzy Modeling (RBMTF). The RBMTF was trained and tested by using MATLAB a personal computer. L/D, ksi were used as the RBMTF input parameters, while the exergy efficiency was the output parameter. The actual values and RBMTF results show that RBMTF can be successfully used for the performances of exergy efficiency of counterflow Ranque-Hilsch vortex tube. L/D, ksi were used as the RBMTF input parameters, while the exergy efficiency was the output parameter. The actual values and RBMTF results show that RBMTF can be successfully used for the performances of exergy analysis of counterflow Ranque-Hilsch vortex tube.