The study of marine ash layers is important for identifying explosive eruptions and their possible impact on the marine environment. In the Philippines, there is additional benefit because tephra are not well preserved on land due to extensive erosion. Here we focus on three tephra layers (1-2 cm thick) preserved in a 960 cm-core, MD06-3057, from the Sibuyan Sea taken during the 2006 Marco Polo II cruise. The topmost light brown layer overlies the second and third dark gray to black layers. Planktonic foraminifera, retrieved from sediments below the first and third tephra layers, were dated using AMS C14 yielding ages of 5840 ± 60 years and 5950 ± 65 years, respectively. Highly vesiculated glass fragments with bubble wall structures were obtained from all intervals and were analyzed by electron microprobe. Physical characteristics and preliminary major element analysis show that the glasses are constrained to two compositional groups. The glasses from the thicker, light-colored ash layer is rhyolitic (69-74 SiO2 wt%); those from the thinner, darker ash layers are andesitic to dacitic (55-64 SiO2 wt%). Data for each ash layer form relatively tight clusters on incompatible element discrimination diagrams implying an eruptive rather than turbidite origin for the layers. The rhyolitic ashes have compositional affinity with post-caldera deposits from the Bulusan Volcanic Complex in the Bicol segment of the Eastern Luzon arc, located ~190 km to the east of the core site. In contrast, the glass compositions of the andesitic to dacitic tephra are distinct from the major element compositions of the Eastern Luzon arc volcanoes. The occurrence of three tephra layers, within a short ~100 year interval suggests that very explosive eruptions have affected the Sibuyan Sea basin and adjacent islands, since ~6000 years ago. This could have had a significant impact on the marine environment, as shown by the change in the size of planktonic foraminifera before, and after the eruption (i.e., smaller planktonic foraminifera within the ash layer).