The characteristics and changes after methylphenidate treatment of executive functions were conducted. Forty elementary school children, over 85 in intelligence quotient, were selected as experimental group. They are diagnosed to have Attention Deficit Hyperactivity Disorder (ADHD). 40 normal control group were also selected. For comparing of executive functions, ADHD subjects were tested executive functions before and 4 weeks after methylphenidate. Normal control group were also tested. Several behavioral checklists were used, and Kaufman Assessment Battery for Children, Conners Continuous Performance Test, Stop Signal Task, Trail-Making Test (patr B), and Maze test were used. The executive functions and intelligence of ADHD were generally lower than normal control group. On CPT, ADHD showed significantly lower performances in commissions, hit reaction time standard errors, variability of standard errors, and attentiveness. On SST, ADHD presented significantly lower performance in probability of inhibit, stop signal reaction time, Z Score of relative finishing time, Mean delay time on each block, and primary standard deviation. On WCST, ADHD had meaningfully lower performance in total corrects, total errors, nonperseverative errors, completed category, and trials to 1st category completed. After medication, intelligence was not changed, but simultaneous processing ability was improved significantly. And the behavioral problems were improved, but still had differences comparing to control. Commission of Conners' CPT, all aspects of SST and total corrects of WCST were improved.