A detailed analysis of high-resolution, multi-beam bathymetric data around Weno Island (Chuuk) reveals very complex seafloor topography caused by build up or growth of coral reef associated with the Holocene sea-level rise. Weno Island is surrounded by fringing reefs, below which the seafloor steeply descends to 1520 m in water depth. Except the eastern tip of Weno Island, the seafloor gradually deepens to 40 m in water depth. This area is characterized by very complex seafloor morphology due to the presence of small-scale coral-reef mounds. At the eastern tip of Weno Island, the seafloor is reef foreslope with slope gradient of 8.2. The eastern part of the study area is about 6080 m deep, and shows slightly irregular mound-like seafloor morphology with very gentle slope gradient. The irregularly mound-like seafloor probably reflects remnants of coral-reef mounds formed during early Holocene sea-level rise. The complex seafloor morphology obtained by multi-beam echo sounder can not be recognized in the published nautical chart.