A number of new geological structures have been revealed in the Great Nicobar Island, Indian Ocean, from the analysis of airborne synthetic aperture radar (SAR) data. The advantages of SAR images for mapping geological structures over other images for the Great Nicobar Island, the southern most island of Andaman-Nicobar arc, have been highlighted. A visual analysis of lineaments in the southern part of the Great Nicobar Island using SAR and Landsat TM colour composites, TM bands 2, 3, and 4, and TM bands 4, 2 and SAR, reveals a wealth of structural information not shown on previous maps. Other identified features include lithological units derived from landforms, northwest-southeast trending faults, faults trending towards the mouth of Galathea river, the graben valley, and many other new faults. The geological features reported in this work were verified using limited ground checking.