Abstract: Insitu measurements of settling velocities were conducted at Xuliujing in Changjiang Estuary during a flood tidal and medium tidal from Sept. 2007 to Oct. 2007. An OBS3A and a LISST100 (Type B) were used together with sufficient water samples to estimate the settling velocity of suspended sediments. Based on the results of measured relationship between the average floc size and floc density, improvement on the original approach was implemented to relax the basic assumption: (1) floc density are the same for all floc size; (2) the volume of void water was included. Thus a better settling velocity of suspended sediment can be estimated.