In this paper, strain gradient thermo-elasticity formulation for axisym- metric Functionally Graded (FG) thick-walled cylinders is presented. For this purpose, elastic strain energy density function is considered to be a function of gradient of strain tensor in addition to the strain tensor. The material properties are assumed to vary according to a power law in radial direction. Using the constitutive equations and equation of equilibrium in the cylindrical coordinates, a fourth order non-homogenous governing equa- tion for thermo-elastic analysis of thick-walled FG cylinders subjected to thermal and mechanical loadings is obtained and solved numerically. Re- sults show that the intrinsic length parameter a ects the stress distribution in FG thick-walled cylinders greatly and increasing the intrinsic length pa- rameter reduces the maximum radial and hoop stresses. Also, the effect of FG power indices on the radial and hoop stresses are studied.