Providing quantitative information on expected flood damage due to climate change is essential for minimizing the future risk through climate change adaptation and mitigation measures. Understanding changes in flood damage in the future due to climate change impact considering regional or local characteristics is also crucial for better manage flood risk in the future. However, the climate change impact on flood damage to exposed elements and the effectiveness of our effort of climate change mitigation and adaptation to build resilient society for future are still not well understood. We thus focused on quantitative assessment of flood damage under climate change with different scenarios of projected population in the future, focusing in the Solo River basin, Indonesia. Flood damage was quantitatively assessed using the hydrologic-hydraulic numerical model and depth-damage flood loss model. Flood damage was assessed focusing on damage to residential buildings and contents for the past and future periods using MRI-AGCM3.2S climate model outputs. The social flood exposures such as number of exposed population and inundated houses in the flood-prone areas were also analyzed. Results show that large areas will be frequently flooded with greater flood inundation volume in future due to climate change impact. The residential building and content damage in the study basin may increase in future by more than twofold times due to climate change (increase by 121–259%, depending on population growth) if climate change mitigations and adaptations are not implemented. The results presented in this study also provide evidence-based information for establishing flood preventive and adaptation measures.