ABSTRACT: A detailed study on radiolarian biostratigraphy and paleoecology has been carried out from three outcrops on Havelock Island, belonging to the Ritchie's Archipelago of Andaman and Nicobar Group of islands. Though most of the radiolarian taxa aremoderately preserved, it was possible to demarcate an age ranging from late early to early middle Miocene based on index radiolarians of RN4 andRN5 zones. An attempt has been made to correlate the radiolarian events recorded herein with earlier reports on radiolarians from different DSDP, ODP, and IODP sites of the Indian Ocean and the onshore sections of different islands of the Andaman and Nicobar Basin. A total of 119 radiolarian taxa belonging to 70 genera have been recorded in the present study, out of which 4 species are being reported for the first time from the northeastern part of the Indian Ocean. Diversity analyses were performed to deduce the Shannon Diversity Index, Simpson Index, Margalef Richness, and Pielou's Evenness. The Water Depth Ecology index (WADE) has been analyzed for a better understanding of the paleoecological perspectives, and the Nassellaria-Spumellaria ratio of each outcrop has been calculated to ascertain the water depth. Comparison of the data obtained from diversity analysis and WADE index provides a clear picture of the environment during the late early to early middle Miocene. The overwhelming dominance of warm species of radiolarians may be linked to the Miocene Climate Optimum (MCO) event.