Preliminary evidence suggests that handwriting difficulties are common to children with Attention Deficit Hyperactivity Disorder (ADHD). However, the nature of the task-specific impairments is needed to be clarified. The aim of this study was to describe handwriting capacity in ADHD children without DCD and identify underlying factors of performance by use of outcome-oriented assessments and a digitizing tablet. Twenty-one children with ADHD (8.59±1.25 years) and 21 match controls (8.5±1.08 years) were recruited. Children with ADHD scored lower than controls on Tseng Handwriting Problem Checklist and writing composite of Basic Reading and Writing Test, indicating the ADHD group wrote less legibly. The ADHD group spent more on-paper time to copy 50 Chinese characters and exhibited more writing time during the writing process. The ADHD group scored significantly lower on tasks demanding upper limb and eye–hand coordination and visual-motor integration compared with controls. Furthermore, motor skill and visual-motor integration were positively correlated with the legibility. Motor skill was negatively correlated with writing time, in-air time, and in-air trajectory.