We evaluated the effect of osmotic-release oral system (OROS) methylphenidate on learning skills in adolescents with attention-deficit/hyperactivity disorder (ADHD). In an open-label study, 121 adolescents with ADHD were administered flexible doses of OROS methylphenidate for 12 weeks. The efficacy of methylphenidate on ADHD symptoms was evaluated by ADHD Rating Scale (ARS) and Clinical Global Impression Scale (CGI). Learning Skills Test (LST) was used to measure the learning skills of the participants at the baseline and the endpoint. Continuous performance test, visuospatial and verbal working memory, verbal fluency, and inhibition were evaluated before and after the 12 weeks of treatment. The mean total and subscores of LST were significantly increased after the 12-week treatment with OROS methylphenidate. Executive functions were also improved during the trial, with the exception of inhibition measured by the Stroop Test. To the best of our knowledge, this is the first study to examine the influence of OROS methylphenidate on learning skill. As a result, OROS methylphenidate was effective in enhancing learning skills in adolescents with ADHD.