The purpose of this study was to identify appropriate outcome measures and assess preliminary efficacy of occupational therapy in an equine environment (OT[superscript ee] HORSPLAY) for youth with autism spectrum disorder (ASD). Twenty-four youth with ASD aged 6-13 were randomized to 10 weeks of OT[superscript ee] HORSPLAY or to a waitlist control condition, occupational therapy in a garden. Youth demonstrated significantly improved goal attainment and social motivation, and decreased irritability after OT[superscript ee] HORSPLAY. When compared to the subset of participants who completed the waitlist control condition, the OT[superscript ee] HORSPLAY group still demonstrated significant improvements in goal attainment. This study provides preliminary evidence that horses can be integrated into occupational therapy for youth with ASD to improve social and behavioral goals.