Lassul Bay is a bay of East New Britain Province, Papua New Guinea, opening into the Bismarck Sea. It is located in the north-western part of New Britain, to the west of Ataliklikun Bay on the Gazelle Peninsula. The communities around Lassul Bay are incorporated into the twenty-one wards of the Lassul-Baining Local-Level Government (LLG) including the settlement of Lassul. The land around the shoreline is swampy and the area has a history of plantation cultivation. The area was invaded in February 1942 by the Japanese during the Battle of Rabaul.