Phragmites australis is one of the most widely distributed plant species and plays an important socio-ecological role in riparian areas. Previous studies have assessed the ecology of Phragmites australis in natural habitats; however, very little is known about its ecology in urbanized areas, where plants are typically exposed to high levels of disturbance. We conducted a field survey to determine the distribution pattern of riparian communities containing Phragmites australis and the variation in the characteristics of Phragmites australis in urbanized areas along the Shonai River, Japan. The distribution of Phragmites australis was investigated in six riparian plant community types with different species compositions. We found increases in the height, stem diameter, and leaf area with increasing coverage of Phragmites australis in some plant communities; however, some communities displayed the opposite pattern, probably because of variations in the interactions between the vegetation and surrounding environment. Among all of the environmental factors, soil properties were the major factors affecting the characteristics of Phragmites australis (32.7% variance). With regard to the environmental variables, the soil water content, total nitrogen, soil organic carbon, and electrical conductivity had significant effects (P <0.05). We found that riparian plant communities presented different structure and composition within different location and land use type, and differences in environmental factors caused by urbanization process influenced significantly on Phragmites australis community and individual.