Abstract: Four drilling cores were collected from coastal lowland of Bohai Bay, and AMS 14C dating method was used to study the age of the second marine layer in coastal low land of Bohai Bay. The dating results of the samples collected form the second marine layer show that the ages are all older than 43.5ka BP, which indicates that the formation of the second marine layer occurred in early MIS3 or MIS 5 rather than 23~39ka as previously considered. Based on previous stratigraphic studies, the authors hold that systematic investigation should be carried out for the age of the second marine layer on coastal lowland of Bohai Bay.