The research was aimed to observe the characteristic of Ganggang sub-watershed in Bojonegoro regency. Several characterstics of Ganggang sub-watershed that observed in this study were (1) land use, (2) topography, (3) shape of the Ganggang sub-watershed, (4) local drainage system, and (5) land use coefficient. Field study observation and literature review were conducted to support this study. The results shown that Ganggang sub-watershed is characterized by several characteristics such as the majority of land use is paddy field, it has very flat topography, the sub-watershed is radial shape, it has medium drainage system, and land use coefficient of 0,2. These characteristics influence the regular flooding in Ngulanan, District Dander of Bojonegoro regency.