Electronic Journal of Differential Equations, Vol. 2010(2010), No. 46, pp. 1-14. Title: Steady-state thermal Herschel-Bulkley flow with Tresca's friction law. Authors: Farid Messelmi (Univ. Zian Achour de Djelfa, Algeria) Boubakeur Merouani (Univ. Ferhat-Abbes de Setif, Algeria) Fouzia Bouzeghaya (Univ. Ferhat-Abbes de Setif, Algeria) Abstract: We consider a mathematical model which describes the steady-state flow of a Herschel-Bulkley fluid whose the consistency and the yield limit depend on the temperature and with mixed boundary conditions, including a frictional boundary condition. We derive a weak formulation of the coupled system of motion and energy equations which consists of a variational inequality for the velocity field. We prove the existence of weak solutions. In the asymptotic limit case of a high thermal conductivity, the temperature becomes a constant solving an implicit total energy equation involving the consistency function and the yield limit. Submitted January 16, 2010. Published April 06, 2010. Math Subject Classifications: 35J85, 76D03, 80A20. Key Words: Herschel-Bulkley fluid; thermal friction law; variational inequality; weak solution.