This MS Excel dataset contains tephra depth and age data from ocean drilling expeditions around Japan. IODP, ODP and DSDP shipboard core description records were examined for mentions of volcanic ash, tephra etc., according to criteria described in Mahony et al. 2014. Data are from shipboard visual core descriptions of ocean drilling expeditions located within a few hundred km of Japan. Cores without published age-depth data are not included in this dataset. The expeditions occurred between 1973 (DSDP 31) to 2013 (IODP 346). Tephra layers are dated as being deposited between 0.003-18.5 Ma. This data will be of interest to volcanologists or anyone interested in the location of volcanic ash layers within IODP cores.