In this paper, modification of Steensen's method with eight-order convergence is presented. We propose a family of optimal three-step methods with eight-order convergence for solving the simple roots of nonlinear equations by using the weight function and interpola- tion methods. Per iteration this method requires four evaluations of the function which implies that the eciency index of the developed meth- ods is 1.682. Some numerical examples illustrate that the algorithm is more ecient and performs better than other methods.