ABSTRACT This study aimed to evaluate the efficacy of a dog-assisted intervention program in occupational therapy (OT) sessions in the treatment of children with Down syndrome (DS). A randomized clinical trial was conducted with 14 children with DS (9–12 years old) randomly distributed into two groups: control and experimental. Both received 12 OT sessions, one per week. The experimental group also received dog-assisted therapy. To evaluate the effects of the program, the Beery-Buktenica Developmental Test of Visual-Motor Integration (Beery VMI), the Test of Playfulness (ToP), an ethogram of positive and negative social behaviors, and comparisons of vasopressin levels in the urine of children upon awakening and after sessions were used. The results showed that after the conventional intervention, the control group had a significant increase in visual perception and attention scores. The experimental group showed a significantly higher frequency of satisfaction and interactivity behaviors. We found that the presence of the dog maximizes the social skills of children with DS and increases their engagement in positive social interactions; however, conventional OT sessions were more effective with visual-motor performance. No physiological changes were observed in either group after the intervention.