Although a considerable body of research with samples from Western cultures shows that having siblings influences children's theory of mind (ToM) understanding, research with samples from other cultures does not always support such findings. The current experiment was designed to examine in detail how family and social environment influence ToM competence in a group of Iranian children from various socioeconomic backgrounds. The participants were 142 preschoolers (4-5 years old) from high-SES (socioeconomic status) urban (n = 33), low-SES urban (n = 37), and rural villages (n = 72). The results failed to show any significant differences between children's scores on ToM measures among the three subsamples, despite the differences between the number of siblings and playmates and the divergent family backgrounds and social experiences of these children. As such, no significant correlation was found between the number of siblings or playmates these children had and their ToM understanding. However, the number of days children spent playing with peers, and the level of parental interference in siblings' conflicts, was correlated with children's ToM understanding. The implications of these results are discussed.