A social vulnerability assessment was conducted to identify which of the watersheds in the Island of Negros, Philippines are most likely to be negatively affected by flood based on the underlying social and demographic characteristics of the population located in flood-prone areas. Assessment at a watershed scale is a challenge considering that it is a hydrologic unit, while the population relies on a political unit. To increase accuracy and address comparability of data, the assessment was first conducted at the barangay level covering 199 villages using government data which were aggregated for the final assessment of 33 major watersheds. An indicator-based approach utilizing 19 indicators was used to capture the level of exposure, sensitivity, and adaptive capacity of the communities, while an index-based method was used to establish the differential social vulnerabilities across barangays and watersheds through a flood social vulnerability index (FSVI). A spatial analyst tool was used to compute the FSVI for easier representation of numerical values in a spatial map and five different vulnerability formulas were compared. The FSVI values revealed that watersheds have low vulnerability due to highly resilient populations attributed to existing government programs for disaster preparedness, response, and recovery, as well as available evacuation centers, medical services, and trained rescue volunteers. Watersheds were then prioritized and clustered according to their level of vulnerability for management intervention of the provincial government.