Background Improving memory is an indicator of treatment in children with Attention Deficit Hyperactivity Disorder (ADHD). Objective The present study aimed to compare the effectiveness of Computerized Cognitive Rehabilitation Training (CCRT) , nutrition supplementation intervention, and both combined on the improvement of Working Memory (WM) in children with ADHD. Methods This was an experimental research with pre-test and post-test, follow-up and control group design. The statistical population included all of the elementary school girls of Tehran City, Iran. Using multilevel clustering, 66 children with ADHD were considered, of whom, 52 were selected for study participation and assigned into 4 experimental and control groups, each consisting of 13 individuals. SNAP-IV and clinical interviews were employed to diagnose ADHD. The Raven's Standard Progressive Matrices was conducted to measure the participants' intelligence level. The study participants were matched in age, Intelligence Quotient (IQ), and the gravity of ADHD symptoms. In group one, 22 sessions of 45-minutes of CCRT were performed using Captain's Log software. The second group received zinc, vitamin B6, and omega-3 for 4 months. In the third group, the first phase of the administration of zinc, vitamin B6, and omega-3 supplements was performed; after 15 sessions, CCRT was performed and obtained by the N-back test. Data were analyzed using repeated measures analysis of variance by SPSS. Findings The obtained results represented the increased mean score of the improvement of WM in the intervention groups, compared to the control group. However, there was no significant difference in WM score between the intervention groups. Conclusion CCRT and nutrition supplementation intervention improve WM in children with ADHD.