Gravity anomalies over the western Walvis Ridge are well explained by a model of the regional depression of the rigid lithosphere under the load of the ridge. Computation of the best-fitting flexural rigidity yielded small scatter about a single value for all profiles across the ridge. Depending on the value adopted for the density of the ridge; an estimate of the rigidity ranges from 2¿1028 to 8¿1028 dyne-cm. The values computed are an order of magnitude lower than those published for the Hawaiin-Emperor seamount chain in the central Pacific Ocean. This fact cannot be attributed to the change in the effective flexural rigidity with time of loading, since we compare the segments of the Walvis Ridge and of the Emperor chain, which are of similar age. The difference in rigidity found favors the formation of the Walvis Ridge on relatively thin lithosphere close to the axis of the Mid-Atlantic Ridge, while the Hawaiian-Emperor chain was produced on old lithosphere far from the East Pacific Rise crest.