The SW Indian Ocean is characterized by the presence of several aseismic features. The Mozambique Ridge, an elongated feature lying roughly parallel to the SE coast of Africa, is by far the least known of those structures, mainly due to the scarcity of marine data. To date, the crustal nature and the origin of the ridge are still controversial points. Since knowledge of the origin of the Mozambique Ridge is important for a better understanding of the evolution of the SW Indian Ocean, the isostatic response of the lithosphere beneath the ridge is analysed in order to characterize its effective elastic thickness and the emplacement process of the feature. Two different approaches are applied, the direct computation of the geoid anomaly over the ridge, by means of a 2.5-dimensional method, and the computation of the admittances between the bathymetry and both the geoid and gravity anomalies. Both approaches point to a local isostatic response of the lithosphere. The crustal thickness beneath the Mozambique Ridge ranges from 17 to 30 km and the average density, from 2.78 to 2.7 X lo3 kg m-3, varying with locality,