The mechanical properties of Nickel Titanium shape memory alloy (known as Nitinol) are strongly temperature-dependent. One of those is the temperature-dependent of the yield stress of the phase transformation. The relationship between the yield stress of the phase transformation and the temperature is well known to obey the Clausius-Clapeyron equation. For the application of Nitinol it is very important to determine the parameters in Clausius-Clapeyron equation. In this study two different approaches were utilized to determine the parameters. One method is to conduct the uniaxial mechanical tests at different temperatures and the parameters were obtained directly from the stress-strain curves; another method is to calculate these parameters by using the phase transformation enthalpy measured by Differential Scaning Calorimeter (DSC) and the phase transformation strain measured by the mechanical tests. Different types of material, tubing, sheet and wire were utilized in this study and the Clausius-Clapeyron equation determined by the mechanical and thermo-mechanical approaches shows a very good agreement.