Abstract: The geological setting and occurrence characteristics of natural gas hydrate in the eastern Nankai Trough offshore Japan have been analyzed and summarized based on the research of gas hydrate drilling expeditions and the Integrated Ocean Drilling Program conducted in this area. As part of the convergent continental margin with strong tectonic activity, the Nankai Trough has well-developed fault and fracture systems, and is rich in gravity flow sediments. Especially in the continental slope of the northern trough with water depth shallower than 2 000 m, a series of fore-arc basins exist, filled with widely distributed unconsolidated Quaternary sediments. The deposition rate of these young sediments is rather high, providing favorable conditions for the formation of gas hydrate. Analyses of the drilling cores taken from this area indicate that the gas hydrate is type I, comprising 99.9% or more methane. The carbon isotopic analysis shows that methane forming the gas hydrate is typically microbial. The gas hydrate occurs commonly in a dispersive state, filling in the pores of the sediment, preferentially accumulating in the sand-rich sediments. The hydrate saturation in the sand-rich intervals is commonly 50%-60% and can reach as high as 80%-90%; whereas the hydrate saturation in the shale layers is extremely low.