The present study examined the role of IQ and the Theory of Mind understanding in children with an autism spectrum disorder and down syndrome. Sixty-six Swedish children with ASD (n = 26), DS (n = 18), and typically developed group (n = 22) ranged between 6 and 12 years old were compared on ToM tasks consisted of standard ToM and IQ tasks. SPSS 25 program was used to analyze data. The results indicated that individuals with ASD reach a better understanding of first-order ToM tasks than children with DS. This picture was the same in the TD group to show better ability than children with ASD and DS on first-order tasks, except one task which was not found significant differences. To employ second-order TD performed better than clinical groups, while, there was no significant difference between ASD and DS. The scores for the third-order task in children with ASD were significantly better than children with DS.