BACKGROUND: Supervised injection facilities (SIFs) have not yet been integrated into Iran's harm reduction programs. This study aimed to report the extent to which people who inject drugs (PWID) in Iran are willing to use SIFs. METHODS: Participants were recruited from 11 major cities using respondent-driven sampling. Willingness to use SIFs was defined as a three-level categorical variable: low, moderate, or high. RESULTS: Of 2,490 PWID, 52.8% and 23.8% reported high and moderate willingness to use SIFs, respectively. PWID with a history of homelessness (relative-risk ratio (RRR): 2.22, 95% CI: 1.76-2.80), incarceration (1.86 [1.48-2.35]), hepatitis C infection (1.49 [1.13-1.97]), and non-fatal overdose (2.30 [1.69-3.13]) were more likely to be willing to utilize SIFs. Willingness to use SIFs was also higher among PWID who reported recent public injecting (2.24 [1.70-2.97]), daily injection (1.82 [1.35-2.45]), stimulants injection (2.39 [1.41-4.07]), syringe sharing (3.09 [1.23-7.74]), harm reduction services utilization (2.80 [2.13-3.68]), and food insecurity (8.28 [5.43-12.63]). CONCLUSION: The majority of PWID in Iran expressed willingness to use SIFs, in particular, those who were involved in higher-risk injection practices, dealing with structural risks, and had experienced drug-related harms. SIFs represent critical opportunities to deliver comprehensive harm reduction services to improve the health and well-being of PWID in Iran.