We examine the stabilization of the two typical moduli, the length rho of the 11th segment and the volume V of the internal six-manifold, in compactified heterotic M-theory. It is shown that, under certain conditions, the phenomenologically favored vacuum expectation values of rho and V can be obtained by the combined effects of multi-gaugino condensations on the hidden wall and the membrane instantons wrapping the three-cycle of the internal six-manifold.