The therapeutic potentials of probiotics in autism spectrum disorder (ASD) remains controversial, with the only existing systematic review on this topic published in 2015. Results from new trials have become available in recent years. We therefore conducted an updated systematic review, to assess the efficacy of probiotics in relieving behavioral symptoms of ASD and gastrointestinal comorbidities. Our review includes two randomized controlled trials, which showed improvement of ASD behaviors, and three open trials, all which exhibited a trend of improvement. Four of these trials concluded from subjective measures that gastrointestinal function indices showed a trend of improvement with probiotic therapy. Additional rigorous trials are needed to evaluate the effects of probiotic supplements in ASD.