Magnetotactic bacteria produce intracellular crystals magnetic minerals with precisely controlled size, morphology, and stoichiometry, specifically magnetite or greigite. These magnetotactic bacteria are widely observed in aquatic environments and remains preserved in the sediments as magnetofossils that record ancient geomagnetic field and paleoenvironmental variations. Although the globally importance of the biogeochemical remanent magnetisations and the useful information of the magnetofossils provide about paleoproductivity or paleoenvironmental is very limited. Magnetofossils have been reported from equatorial Indian and Neo-Tethys Oceans during the Middle Eocene Climatic Optimum (MECO, ~40 Ma). The MECO event is a strong transient warming event (global temperature increase 4-5°C) that has recognized in the oceanic records. Here, using environmental magnetism and first order reversal curves (FORC), we present evidence for abundant magnetofossils during the MECO event from Neo-Tethys and Indian Oceans sections.