Yodogawa and Yamatogawa are two largest rivers which flow in Osaka plain, Kansai district, southwest Japan. Osaka which is a mega city is located near these rivers. The content analysis and elution (liquate out) test on the heavy metals of Cd, CN, Pb, Cr, As, Hg, Ni, Zn and Cu were carried out for environment assessment. The samples were extracted from the river sediment at intervals of several km. We can not detect serious human impact by heavy metals from the all sampling points of both rivers. But slightly higher points on Hg, Pb and Cr are detected at the mouth of both rivers.