We propose a symbolic formulation for computing eigenvalues, eigenvectors and generalized eigenvectors of rational matrices. Based on the Frobenius normal forms of matrices, our formulation constructs the eigenvectors without solving a system of linear equations by Gaussian elimination over an algebraic extension field. The experimental results show that our algorithm is more efficient than a conventional method implemented on the existing computer algebra systems. Although both Reduce and Maple failed for middle-sized matrices because of the memory problem, our program succeeded in solving the eigenproblem for much larger matrices.