Relationships between variations in river topography, such as riffles and pools, and fish, benthos, etc., have long been studied. The topographical classification of riffles and pools, however, is still conducted qualitatively. To take measures for the restoration or improvement of habitats, it is necessary to quantify these relationships and explain them in hydraulic terms. Meanwhile, studies on river -bed morphology have been conducted from the sediment hydraulics viewpoint, allowing for expression with physical indices. This paper examines the quantitative classification of riffles and pools of mountain streams, based on the findings of sediment hydraulics, to clarify their characteristics.