Attention deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterized by inattention, hyperactivity, and impulsivity. ADHD symptoms not only impact patients and their families but also impose societal costs. Current treatments for ADHD, including environmental adjustments and medication, are symptomatic and require long-term management. Recently, the link between gut microbiota dysbiosis and various psychiatric and neurological disorders has become evident. The effectiveness of fecal microbiota transplantation (FMT) from healthy individuals in treating autism spectrum disorder, a neurodevelopmental disorder related to ADHD, has been demonstrated. However, despite suggestions of a relationship between ADHD and gut microbiota, few studies have explored the efficacy of FMT for ADHD. In the current study, we used 16S rDNA analysis to show that ADHD-like model rats possess a gut microbiota that is distinct from that of healthy rats, and we demonstrated that FMT from healthy rats improved hyperactivity in ADHD-like model rats. Our findings suggest that differences in gut microbiota underlie ADHD-like behaviors and that FMT may be an effective treatment for ADHD.