Mountain streames are different in many aspects from those on a plain. For example, channel slopes are very steep, grain sizes on the stream beds are large and have very wide distribution, relative depths of flows are always small, and so on. These typical differences in nature should result in different resis-tance and sediment transportation characteristics from those on plain streams whose characteristics have been investigated. Recently, the authors have derived an equation to predict the critical condition for the initiation of motion of uniform bed materials on very steep channels. This paper discusses, as a developement of the previous investigation, the critical condition for the initiation of motion of mixtures of wide range grain sizes. Resistance characteristics corresponding to the roughness of bed surface are also discussed. Non-dimensional threshold shear stress for each grain diameter in the mixture increases with increasing relative roughness and under a constant relative roughness that for smaller grain diameters are larger than that for larger grains. The threshold shear stress for the mean diameter size grains in the mixture is larger than that for the same size grains in the uniform bed materials due to the sheltering effect of larger grains.