Transboundary glacial lake outburst floods (GLOFs) pose severe risks to downstream communities and infrastructure across international borders. However, previous GLOF research has largely overlooked the transboundary aspects of national and sub-national level GLOFs, focusing instead mostly on inventorying glacial lakes and assessing their hazards. The lack of cross-border coordination could have dire consequences for vulnerable communities and potential disaster preparedness. Assessing risk perception and vulnerability among downstream populations exposed to GLOFs is crucial for effective disaster risk reduction and management. This study examined the risk perception and vulnerabilities of Nepali communities in Bhotekoshi/Sunkoshi (Poiqu in Tibet) and Trishuli (Gyirong in Tibet) river basins, exposed to transboundary GLOFs originating from Tibetan basins. Household-level data were collected from 90 respondents in the villages along those two basins. The findings highlight high risk perception in the Bhotekoshi basin and medium perception in the Trishuli basin, along with corresponding vulnerability levels. Key factors influencing risk perception and vulnerability are explored, emphasizing the need for public awareness and policy formulation at national and regional levels. To reduce vulnerability to transboundary GLOFs, extending early warning systems, enhancing cross-border cooperation, supporting socioeconomically disadvantaged populations, and ensuring resilient infrastructure are essential.