Background: Developmental delay is one of the most commonproblems of children referred to pediatric neurology clinics.While there are reports on rehabilitation and its effects,limited studies are available to delineate pharmacotherapy ofsuch children. Because many children with developmental delayhave abnormal findings in electroencephalography, weaimed to treat a group of these children, who were seizure freewith sodium valproate to find the effect of sodium valproate inimproving the developmental delay.Methods: We included patients referred to Mofid Children’sHospital for developmental delay who had no organic or brainstructural diseases, genetic or metabolic disorders, or intrauterineTORCH infection; however, the patients had abnormalelectroencephalograms (without seizure). After clinical, paraclinical, and neuroimaging evaluations, the patients were dividedinto two groups; those receiving treatment with sodiumvalproate and rehabilitation (experimental group, 25 patients),and those having only rehabilitation (control group, 25 patients).The patients were followed up and assessed at 6, 12,and 18 months after initiation of the study. The data obtainedwere analyzed using SPSS software.Results: All patients in the experimental group had normalelectroencephalograms after 18 months of treatment. Differencesin the scores of developmental quotient in both groups,before and after treatment were significant.Conclusion: Sodium valproate along with rehabilitation wasvery effective in the improvement of speech, mental, and behavioraldevelopment.