The occurrence of ferromanganese micronodules, hitherto unreported from any fan-valley system of the world, has been recorded from over 0.22 million km 2 area located in the middle fan region of the Bay of Bengal. Botryoidal and spheroidal are the two dominant morphological forms observed in the eastern and the western bay respectively. The preliminary results suggest that Mn released from the smectite clay mineral and early diagenesis are the responsible for their formation.