Abstract: Grain sizes are analyzed for the sediments taken from two drill holes in the Shenhu area of northern South China Sea in order to understand the relationship between the saturations of gas hydrates and the grain-size of the sediments. Results suggest that the silt fraction is the dominant component of gas-hydrate-bearing sediments in the studied area, making up about 72%~82% of the sedimentary grains. The second component is clay, which is usually less than 30%; whereas the sand fraction is less than 10%. The Grain size distribution pattern of the gas-hydrate-bearing sediments is similar to the non-gas-hydrate-bearing sediments above and below. Coarse silt(0.063~0.032 mm) and sand(0.063~0.5 mm) are usually high in gas hydrates saturations, further suggesting that coarse sediments are more favorable for the formation of gas hydrates.