It is an important subject to evaluate sediment transport rate in river management works. Especially in a large scale river like Ishikari, establishment of a tool to predict the sediment transport at the estuary is becoming urgent subject from environmental view point. The propose of this paper is to study the effect of the past experienced flood to the grain size distribution of bed material and sediment load. For this propose, data of suspended load observation was collected and the suspended sediment observation was conducted in the Ishikari River. Using these data, and a numerical model, the relationship between suspended sediment load and the discharge history is discussed.