In this paper, the solution of Hammerstein integral equations is presented by a new approximation method based on operational matrices of Chebyshev polynomials. The nonlinear Hammerstein and Volterra Hammerstein integral equations are reduced to a system of nonlinear algebraic equations by using operational matrices of Chebyshev polynomials. Illustrative examples are presented to test the method. The method is less complicated in comparison to others. The results obtained are demonstrated with previously validated results.