Linear instability analysis of a thin layer of viscoelastic fluid flowing down a non-uniformly heated inclined plane is considered. The study is based on the assumption of constant temperature gradient (positive or negative) along the plane. The film flow system is influenced by gravity, mean surface tension, thermocapillary forces acting along the free surface and viscoelastic forces. The role of these forces is investigated by seeking a solution of the stability problem in a series in small wave number. The results show that the critical Reynolds number is influenced by the Reynolds number, the ratio of Marangoni number to Prandtl number, the Biot number, the viscoelastic parameter and the angle of inclination. © 2005 Elsevier Ltd. All rights reserved.