Constitutive relations describing thermomechanical behaviour of shape memory alloys(SMA)are discussed based on Tanaka's model. Special attention has been paid to the isothermal tensile process and the constrained recovery process.The material parameters in the constitutive equations,namely the elastic modulus D,the transformation tensor Ω,and the thermoelastic tensor Θ.are assessed by using experimental date of TiNi alloys.Strong temperature dependencies of D and are found from different experimental stress-strain-temperature relations.