Objective: This study attempted to evaluate the effectiveness of non-verbal motor imitation on length of utterance among 8-16-year-old children with autism spectrum disorders (ASD). Method: The research population included all children with ASD aged 8-16 years living in Miandoab, Iran, in 2016. Thirty children were recruited through convenience sampling and randomly assigned to experimental and control groups. This study had a pretest-posttest design with a control group and follow-up. The Childhood Autism Rating Scale (CARS), a non-verbal motor imitation package, and a package of action pictures were employed for data collection. Data were analyzed using repeated measures ANOVA. Results: The results showed that non-verbal motor imitation significantly increases length of utterance in children with ASD (p<0.01). Conclusion: Because of the benefits of non-verbal motor imitation in the treatment of children with ASD, it is recommended that this method be offered in conjunction with conventional methods to the parents and teachers of these children.