This paper deals with the propagation of Rayleigh waves in a micropolar thermoelastic half space with impedance boundary conditions. The boundary of the half spaceis thermally insulated / isothermal and it is assumed that normal traction, shear traction and shear couple traction at the surface, varies linearly with normal, tangential components of displacement and microrotation respectively. The secular equation for Rayleigh wave with impedance boundary conditions is obtained and this equation is in agreement with the classical secular equation for elastic solid with traction free boundary conditions when micropolar, thermal and impedance parameters are removed. The non-dimensional speed of Rayleigh wave is computed as a function of impedance parameters and presented graphically for a particular micropolar thermoelastic material