Rapid urbanization processes result in the losses of ecosystem services in the surrounding areas of cities and cause ecological risks. Currently, there is a lack of ecological risk characterization methods for urbanized areas based on ecosystem services. This research developed an ecological risk characterization method based on ecosystem service values, which use multiple ecosystem service types as the ecological risk assessment endpoint. Moreover, we applied this risk characterization method to evaluate the ecological risks in Beijing and analyzed the uncertainties and the parameter sensitivities in the risk assessment. The results of the case study show that the ecological risks can be separated into five levels according to the frequency distribution of the ecological risk index values in Beijing in 2015. The mean values of the risk index was 0.64, meaning that the ecological risk was overall at the low level, but very close to the middle level in Beijing. The areas showing low and very low risk levels occupied about 50% of the total area of Beijing, distributing mainly in the west and north of the region; the areas presenting high and very high risk levels accounted for about 20% of the total area of Beijing, which were mainly distributed in the central areas of the region. Overall, the ecological risks exhibited an apparent spatial heterogeneity and urban-rural gradient characteristics in Beijing. Moreover, the ecological risks showed a generally similar declining trend to the artificial surface ratio from the urban areas to the rural areas in space. The spatial pattern of ecological risks implies that the expansion of the urban areas in Beijing caused the decline of the ecosystem services in the surrounding areas, which led to the increase in ecological risks. The proposed ecological risk index exhibits a highly significant linear relationship with ecosystem service equivalent weight factors and therefore, can be used to estimate the total value of ecosystem services. The calculation generates results with small variations using the risk index proposed in this study to estimate the ecological risk in a region with fixed land use composition, meaning that the proposed ecological risk index has a relative high reliability. The method proposed in this study can comprehensively characterize the ecological risks in urbanized areas and generate results that are easy to understand for decision makers, and therefore, has potentials to be applied in the practice of risk assessment and management. Future studies using the ecological risk index we propose need to choose more reliable methods to calculate ecosystem service values, so as to obtain more accurate risk assessment results.