In biological families, parental reflective functioning (PRF), or the parents’ capacity to envision their child as being motivated by internal mental states, is known to facilitate the development of the child’s theory of mind (ToM). Very few studies have investigated the relation between PRF and ToM in adoptive families, and none have simultaneously investigated the role of pre- and post-adoptive PRF. The present study is the first to examine relations between pre-adoptive reflective functioning (RF), post-adoptive PRF and children’s ToM acquisition in a sample of internationally adopted children and their adoptive parents (48 children; 14 girls and 34 boys). Specifically, we investigated whether the relation between pre-adoptive RF and ToM was mediated by PRF assessed when children were aged 3.5–4 years, and whether these relations were moderated by age at adoption, which served as a proxy for early adversity. Results indicated that none of the PRF dimensions mediated the relation between pre-adoptive RF and ToM. However, pre-adoptive RF and PRF both independently predicted ToM. Moreover, age at adoption moderated these associations, with both pre-adoptive RF and dimensions of PRF assessed at child age 3.5–4 years being related to ToM only in children who were adopted at an older age (≥18 months).