Autism Spectrum Disorder (ASD) is a constellation of social communication problems in addition to unusual and repetitive behaviors. In this review, we aimed to investigate the effects of probiotics, prebiotics or synbiotics on gastrointestinal (GI) and behavioral symptoms of ASD. We searched the relevant literature in several electronic databases. In total, 344 children with ASD were investigated in this review. The results of this review demonstrated significant effects of the intervention with probiotics and prebiotics on all domains of Autism Treatment Evaluation Checklist (ATEC) score. There were also different reports about their beneficial effects on the improvement of gastrointestinal symptoms, although a need for more clinical trials with the same doses and types of microorganisms is also highlighted.