An inverse analysis utilizing the conjugate gradient method of minimization and adjoint equation is used successfully to solve the inverse problem in estimating the temperature‐dependent thermal conductivity of a composite material. No prior information is available on the functional form of the unknown thermal conductivity in the present study, thus, it is classified as the function estimation in inverse calculation. The accuracy of the inverse analysis is examined by using the simulated exact and inexact measurements that were obtained within the medium. ©1995 American Institute of Physics.