Bull. Jpn. Soc. Fish. Oceanogr. 75(4), Page 221-226, 2011   Residual current estimated from ADCP observation in Sendai Bay Shigeho Kakehi† Tohoku National Fisheries Research Institute, Fisheries Research Agency, Shiogama, Miyagi 985-0001, Japan † e-mail: kakehi@affrc.go.jp Repeated observations with ship-mounted ADCP were acquired in Sendai Bay. As the duration of the observations was 9 h, which is shorter than semi-diurnal tidal period, residual current was estimated from the regressed current by the least squares method using the time derivative of predicted tide. The correlation coefficient between observed and regressed current was 0.996 at most. This indicates the de-tiding method of this study is valid. Southward current was dominant in the estimated residual current and the maximum residual current exceeded 20 cm⋅s-1. Geostrophic current calculated from observed temperature and salinity corresponded to the residual current. The residual current was likely to be driven by density distribution. Key words: ADCP, de-tiding method, residual current, Sendai Bay