At the present it has been clarified that soil masses covered with reeds that had fallen from the banks are not easily transported and still protect banks by reducing the flow velocity surrounding them. Therefore, this study aims to develop riparian protection measures against bank erosion using soil masses covered with reeds by placing them along river bank at an streamwise intervals. Two experiments on erosion have been done by using undisturbed soil masses covered with reeds that were obtained from the field. One is made by observing the erosion of soil masses one by one in a laboratory experiment. The other is made in at a channel for agricultural use of Hii river to observe an erosion of soil masses for longer period by placing some soil blocks longitudinally along the river bank. The reeds' density resisting the erosion of soil mass is found from the experiments. Moreover, it is proved that soil masses covered with reeds can be available for riparian protection for a long period.