Determination of wall heat flux for laminar flow inside a duct from the temperature measurement within the flow is a typical inverse heat convection problem which is ill-posed. In the present paper, an efficient method based on the Karhunen-Loeve Galerkin procedure (Park and Cho, 1996, Chem. Engng Sci. 51, 81-98) is proposed for the solution of this kind of inverse heat transfer problems. Employing the Karhunen-Loeve Galerkin procedure, which is a Galerkin method employing empirical eigenfunctions of the Karhunen-Loeve decomposition, one can a priori limit the function space considered to the smallest linear subspace that is sufficient to describe the observed phenomena, and thus convert a given system into a model with a minimum degree of freedom, resulting in drastic reduction of computation time. The performance of the present technique of inverse analysis using the Karhunen-Loeve Galerkin procedure is evaluated by numerical experiments on the identification of unknown functions of wall heat flux, and is found to be very accurate as well as efficient.