Abstract: Grain-size distribution patterns of the upper 40m of sediments of the core BHS01 are studied to detect the evolutional course of depositional environment of the Bohai Strait. Results show that the mean grain size of the sediments varies from 3.2Φ to 7.5Φ, indicating mixed sediments of silty sand and sandy silt. The sorting of the sediments ranges from 1.3 to 2.5, indicating poor sorting deposits. The skewness of the sediments are mostly dropped in the range of -0.4~3.0, showing a positive and super-positive skewness, while the kurtosis of the sediments varies from 1.9 to 12.4, showing an acute normal distribution. Based on the integrated analysis of grain size parameters, C-M diagrams, scatter diagrams and the changes in grain size with depth, it is concluded that the Bohai Strait was once a high-energy environment. Seven sedimentary units are recognized for the upper part of BHS01, which indicate the evolutional history of the region since Middle Pleistocene from shallow sea facies to fluvial facies, to shallow sea facies again.