One of the main problems in the treatment of rational functions consists in representing them suitably for the purpose of their symbolic and algebraic manipulation. One can approach this problem by means of Hankel matrices if an efficient method for computing ranks is available. In this paper, a modular algorithm for determining the rank of a Hankel matrix with entries that are multivariate polynomials over the integers is presented. The algorithm is based on modular techniques, which consist in computing the rank of Hankel matrices over finite fields by a special algorithm that needsO(n2) arithmetic operations, wheren is the order of the matrix. The general solution is achieved by determining the maximum of the ranks computed over the finite fields.