In this paper, we analyzed the grain size and heavy mineral compositions of 52 surface sediment samples collected from the Kompong Som Bay of Cambodia and the adjacent rivers to depict the marine sedimentary environments and transport processes. Heavy minerals in sediments are dominated by authigenic pyrite, siderite, and tourmaline, with average percentages of 36.52％, 29.02％, and 10.94％, respectively. Two provinces can be divided according to the spatial similarity of minerals. The sediments from Province I, covered by silt grains in the northern bay, are characterized by autogenic pyrite, indicating a weakly reducing environ-ment; whereas in Province Ⅱ, covered by sand grains in the southern bay, the siderite-tourmaline-authigenic pyrite-zircon-hornblende assemblage occurs, indicating a mild reducing environment and locally oxidizing environment. Most of the sediments in the Kom-pong Som Bay are introduced from the Preak Piphot River and Srae Ambel River, except that some of them in the south areas come from coastal erosion. Generally, the sediments are difficult to be transported because of the low sediment loads entering the sea and weak hydrodynamic conditions. However, they are transported from the north to the south during the tide ebbing when the hydrody-namic force is much stronger. The sediment distribution and transport patterns are controlled by many factors, including submarine topography, hydrodynamic conditions, the southwest monsoon, land contours, and sediment supply.