Objective To investigate the effect of methylphenidate on event related potential(ERP) in children with attention deficit hyperactivity disorder(ADHD).Methods Thirty-two children with ADHD(ADHD group)were treated for oral using methylphenidate and observed for 2 hours,scale for the assessment of methylphenidate were evaluated with the P300 ERP in Go/Nogo task.Thirty healthy children(healthy control group) were controls,to compare the differences of ERP main components.Results The latency[(355.16±17.04) ms] and amplitude[(5.88±1.72) μV] of Go-P3 in ADHD group after treatment were significantly shorter and higher than before treatment[(366.66±19.32) ms and(4.82±2.14) μV,Pa0.05],but longer and lower than those in healthy control group[(333.70±23.57) ms and(7.19±1.87) μV,Pa0.05].The amplitude [(6.13±1.68) μV] of Nogo-P3 in ADHD group after treatment were significantly higher than before treatment[(5.04±1.76) μV,P0.05],but lower than that in healthy control group[(8.32±2.03) μV,P0.05].Conclusion Methylphenidate can improve the attention and inhibitive executive functions in children with ADHD.