Communicating sustainability on social media is an effective way to promote this ubiquitous concept to the public. In the Cambodian context, many actors, including the government, local associations, and international non-governmental organizations, use different strategies and frames to circulate sustainability dialogue to the public. As a leading organization for sustainability promotion, the United Nations in Cambodia employs social media, particularly Facebook, to communicate sustainability to its audience. This study aimed to identify the frames used by the United Nations in Cambodia when representing sustainability on social media. An investigation of Facebook usage by the United Nations office in Cambodia showed that the United Nations in Cambodia used seven different frames to represent sustainability on its Facebook page. The majority of the sustainability frames found in this study concerned the general living conditions of the people, indicating a dominant sustainability representation from a social dimension. However, the environmental and economic perspectives of sustainability were underrepresented, which contradicts the current trends in sustainability representation. This study therefore shows that the United Nations prioritizes human welfare and the social aspect of sustainability in the Cambodian context. Further research is needed on how other actors, such as the government and local organizations, frame sustainability on social media.