Recently, the frequency of debris flow hazard has increased in Korea. The debris flow occurring around expressway can cause serious direct and indirect damages not only on cars and drivers on the road but also on national infrastructures. For the effective prevention of debris flow on expressway, potential basin areas with a high possibility of hazard need to be selected and a quantitative risk assessment for those basin areas should be performed. In this study, a risk assessment of debris flow on 1545sites (1093 km) of public expressway was conducted by the risk evaluation method suggested by Korea Expressway Corporation. Based on the risk assessment, basin characteristics of high and low risk areas around expressway were analyzed. Analysis results showed that the basin areas at 507 sites (33%) out of total 1,545 sites were at high risk for debris flow. And they have a higher inclination than low risk area for both average basin area and stream channel.