In this article, using an infinite-dimensional equivariant Conley index, we prove a generalization of the profitable Liapunov center theorem for symmetric potentials. Consider a system ( * )q = −∇U (q), where U (q) is a -invariant potential and is a compact Lie group acting linearly on R n . If system ( * ) possess a non-degenerate orbit of stationary solutions (q 0 ) with trivial isotropy group, such that there exists at least one positive eigenvalue of the Hessian ∇ 2 U (q 0 ), then in any neighborhood of (q 0 ) there is a non-stationary periodic orbit of solutions of system ( * ).