  In this paper, we investigate approximate solutions for nonlinear Fredholm
integro-differential equations of fractional order. We present an operational
Tau method by obtaining the Tau matrix representation. We solve a special class
of nonlinear Fredholm integro-differential equations based on Legendre-Tau
method. By using the Sobolev inequality and some of Banach algebra properties,
we prove that our proposed method converges to the exact solution in L^2-norm.
