Considering the depositional environments and their changes in Gangjin Bay, this study has analyzed in total 35 surface sediments sampled from the bay, in 2000 and 2010. When comparing the sediments of 2000 and 2010, the coarse portion had no significant change, but the portion of the silt and clay changed greatly with respect to the size distribution. Also, the sediments decreased in size during the previous 10 years. The sorting values of the sediments changed to a wide and poor states and the tendency of poor to extremely poor in range. The sediments negatively skewed gradually and became leptokurtic during above years. The result of the T-test (p<.05) preformed in order to estimate the statistical significance of the size distribution and textural parameters in the sediments, the values of mean size, skewness, kurtosis and the contents of silt and clay, changed. Also, the depositional environment changed within the study area. It is considered that the depositional environment of the study area gradually changed due to the controlling factors, such as dam building in upstream areas, tidal velocity changes, straightened streams and linear sea walls.