An iteration method is used to get the eigenvalues of the problem, namely, the laminar flow of power‐law fluids with viscous heat generation between parallel plates. An asymptotic solution for large eigenvalues is developed and it is further used as the initial guess in the iteration scheme for exact eigenvalues. The method used in this paper has the advantages of fast convergence and high accuracy. Also, the method can be applied to any value of the continuous exponentnin the power law without limitation.