Purpose: The purpose of this study was to analyze the impact of the implementation of Picture Exchange Communication System (PECS) on the comprehension of instructions for children with Autism Spectrum Disorder (ASD). Methods: This is a longitudinal study (N degrees 0809/2018). The sample consisted of 20 children with nonverbal ASDs, 15 boys and 5 girls, aged 6 to 12 years, evaluated and diagnosed by a multidisciplinary team, according to the DSM- 5. For assessment of the comprehension of instructions, we used 8 visual instructions and 8 oral instructions were applied at two points in the PECS Implementation Program: early phases II and IV. The program consisted of 24 individual speech therapy sessions with the presence of the family member and obeyed the six phases originally proposed by the PECS Training Manual. Results: There was an expressive increase in the comprehension of all the instructions, in the comparison between the two moments of the study; and in six of the oral instructions (p=0.001) and five visual ones (p=0.002), this increase was statistically significant. Conclusion: It was possible to observe the positive impact of the use of PECS in the comprehension of both visual and oral instructions, showing that this system not only provides an augmentative or alternative communication tool for the child to express himself, but also promotes a significant improvement in the understanding of information contextual.