ABSTRACT. Let (M, g) be a compact orientable conformally flat Riemannian manifold and pXi the minimal eigenvalue of the Laplacian operator for p-forms. We prove that if there exists a positive constant K such that p > Kg, where p is the Ricci tensor of M, then pXi > Kp(n -p + l)/(n -1) f°r eacn P, 1 < p < n/2, (n = dim M); moreover if the equality holds for some p then M is of constant curvature a = K/(n -1).