In order to clarify the sedimentation rate of 210Pbexcess and 137Cs in brackish Lake Obuchi, bordered by nuclear fuel facilities in Rokkasho Village, Aomori, Japan, sediment core samples were collected at three points in the lake, and the rates were calculated by the chronological measurement method using 210Pb and 137Cs. The sedimentation rates were 0.29±0.04 g . cm-2 . y-1 in the estuary of the Futamata River (water depth of 1.2 m), 0.13±0.02 g . cm-2 . y-1 in the 3 m water depth area, and 0.11±0.02 g . cm-2 . y-1 at the center point (water depth of 4.5 m), respectively. The Futamata River estuary was found to be greatly affected by land erosion.