Project closure is a core feature of humanitarian action. However, how decisions to end projects are made, and how closure is planned and implemented, has implications for upholding ethical commitments, and can have positive or negative consequences for affected communities, local stakeholders, and humanitarian organizations and their staff. To better understand the ethical dimensions of closing humanitarian projects, we undertook an investigation of national and international humanitarian workers’ experiences.Guided by interpretive description methodology, we conducted an exploratory qualitative study with two rounds of semi-structured interviews. Four national and five international staff of non-governmental organizations with experience of humanitarian health project closure took part. The participants had diverse professional roles and disciplinary backgrounds. All participants took part in the first round of interviews which focused on experiences and perceptions of ethics and project closure. Analysis of these interviews contributed to the development of a draft “ethics guidance note.” Five of the participants took part in the second round of interviews which focused on receiving feedback on the draft guidance note. We used constant comparative techniques and a recursive approach to data collection and analysis. In this article, we draw on both rounds of interviews to present findings related to how participants understood and experienced ethical responsibilities, challenges, and opportunities for humanitarian project closure.We identified six recurrent ethical concerns highlighted by interviewees regarding closure of humanitarian projects: respectfully engaging with partners and stakeholders, planning responsively, communicating transparently, demonstrating care for local communities and staff during project closure, anticipating and acting to minimize harms, and attending to sustainability and project legacy. We present these ethical concerns according to the temporal horizon of humanitarian action, that is, arising across five phases of a project’s timeline: design, implementation, deciding whether to close, implementing closure, and post-closure.This exploratory study contributes to discussions concerning the ethics of project closure by illuminating how they are experienced and understood from the perspectives of national and international humanitarian workers. The interview findings contributed to the development of an ethics guidance note that aims to support project closures that minimize harms and uphold values, while being mindful of the limits of ethical ideals in non-ideal circumstances.