For predicting the timing or intensity of nitrate loss, sediment yield and flood in Seto Inland Seacatchments, we confirmed rainfall properties there by using hourly rainfall data at Shimo-Kamagari Island andMiyajima Island. The average annual precipitation is about 1100 mm and 1600 mm at both islands, respectively.Total rainfall at the events of more than 30 mm exceeded 50 0f the total annual rainfall at both sites. From theresults analyzed rainfall time, the peaks of rainfall intensity were found around 6 AM and 5 PM. Timing ofrainfall was controlled by rainfall mechanisms and landform characteristics. Maximum hourly rainfall intensitywas similar at both sites during a big event of more than 70 mm.