Aim: Outdoor adventure programmes aim to improve interpersonal relationships using adventurous activities. The current study examined the effectiveness of an outdoor adventure programme in children with autism spectrum disorders (ASD). Method: The study included 51 participants (40 males, 11 females; age 3y 4mo–7y 4mo) enrolled in ASD special education kindergartens. Only the intervention group (n=30) participated in the outdoor adventure programme for 13 weeks, completing challenging physical activities that required cooperation and communication with peers and instructors. The control group (n=21) was not significantly different from the research group in age, sex, cognitive, and adaptive behaviour measures. Results: Outcomes after the intervention revealed significant improvement in social-communication and different directions in the two groups in the social cognition, social motivation, and autistic mannerisms subdomains of the Social Responsiveness Scale. While the group that received an outdoor adventure programme showed a tendency toward a reduction in severity, the control group showed the opposite (p<0.010). Interpretation: The outdoor adventure programme required problem-solving skills and forced the child to communicate in exciting situations. This study suggests that an outdoor adventure programme may be an effective intervention in addition to traditional treatments in young children with ASD. Future studies should examine the outcome of outdoor adventure programmes delivered for longer periods of time and maintenance of the achievements over time.