Ranque-Hilsch Vortex Tube (RHVT) is a mechanic system which can make heating and cooling by using basic heat transfer laws with a compressed fluid. Environmental friendly RHVT is widely used in cooling systems in medicine, electronics, and computer sectors, particularly in the food sector. In this study, the performances of parallel RHVTs in which oxygen (O-2) gas is used were reviewed considering different inlet pressures, nozzle materials and orifice numbers. Test results were modeled by multiple linear regression method and regression equation was derived. Besides, Signal/Noise (S/N) ratios of the designed test results were calculated using Taguchi L16 mix type (4 x 2 2 x 1) orthogonal sequence, and optimum conditions were determined. Throughout the test, hot fluid outlet valve of the counter flow RHVTs having o10 mm inner diameter and 100 mm body length was completely left open. As control factors and levels, four different inlet pressures (200, 350, 500, and 650 kPa), four different number of orifices (three, four, five, and six), and two different nozzle materials (brass and polyamide) were selected. For quality characteristics, maximum temperature gradient ( increment T) was determined. In order to determine the effect rates of the control factors on quality characteristics ( increment T), variance analysis (ANOVA) was applied to test results at 95% confidence level. According to statistical results, it was determined that the response rates of Delta T values from the control factors were determined as inlet pressure, the number of orifices and nozzle material, respectively. Validity of the optimization was checked with confirmation tests, and the optimization proved to be used in evaluation of RHVT performances.