After Merapi eruption in 2010, huge produced material from the eruption was deposited in surrounding the volcano. When the high intensity of rainfall occurred, the material would be flowed down by debris flows. The debris flows took place frequently in almost rivers originated in the volcano and then, they flowed down to the Indonesian sea through main rivers. One of the main rivers is Progo River. River bed material in lower of Progo River would be affected by the debris flows. Therefore, it is important to investigate riverbed material condition due to debris flows after Merapi eruption in 2010. The aim of this research is to compare the characteristics of riverbed material in lower of Progo River, before and after Merapi eruption in 2010.