Objective: The present study aimed to reveal the brain correlates of phonological working memory (WM), dual tasking, and distraction in adult ADHD combined with the effect of polymorphisms of monoamine oxidase A (MAOA rs1137070 Asp470Asp). Method: A total of 29 participants with adult ADHD and 21 controls were recruited. They completed 0-back and 2-back tasks, as wells as 2-back tasks with a dual-task effect or a distracting effect, during functional magnetic resonance imaging scanning. Results: The brain activation of WM in the bilateral inferior frontal lobe, pars opercularis, was higher among the adult ADHD group. The genotype of MAOA significantly interacted with the ADHD effect in the left inferior frontal lobe, pars opercularis. Adults with ADHD had higher activation in the left lingual area in response to the dual-tasking effect. Conclusion: The MAOA polymorphism moderated the altered activation in pars opercularis for WM among adults with ADHD. The higher lingual gyrus activation might indicate that higher attention resources are demanded to sustain the dual-task function of adults with ADHD. (J. of Att. Dis. XXXX; XX(X) XX-XX)