Abstract: The adsorption characteristics of 237 Np on crushed tuff and tuffaceous sand from northeast Japan have been studied using sequential extraction analysis technique. With a large difference in cation exchange capacity (CEC), both materials show nearly same sorptivity for 237 Np. Together with dominance of ion exchange processes in sorption indicated by sequential extraction analysis, it suggests an absence of specific sorption at sites of this kind. It's interesting to find that sorption on Fe Mn oxyhydroxide oxides, defined by our sequential extraction procedure, almost keep constant for both cases, without time dependency. A potential mechanism of surface chemical reaction is deduced. Kinetics with respect to exchangeable and residual portions in tuff and fuffaceous sand confirms that some slow processes are controlling radionuclide sorption.