Background: Diverse cognitive functions and behaviors have been monitored in the two sub-types of attention deficit/hyperactivity disorder (ADHD) including the combined type and the inattentive type. Objectives: Previous studies have shown that ADHD children have problems in visual memory, and short and long-term use of methylphenidate (MPH) improves these functions, but fewer studies have been done on the inattentive subgroup, namely attention deficit disorder (ADD). Due to the different cognitive functions in these two ADHD subgroups, this study was done to investigate the long-term use of MPH on the visual memory of ADD children. Methods: A 4-week experimental clinical trial using MPH (1 mg/kg/dose) was conducted. Participants were 20 children aged 6 -11 years with ADD that came to the Rouzbeh Clinic in Tehran in 2010. Cambridge neuropsychological test automated battery (CANTAB) tests of visual memory were used for assessment. Results: The long-term use of MPH improved 12 aspects of paired associated learning (PAL) such as first-trial memory score, the number of mean mistakes to success and mean efforts to success (P < 0.05). However, MPH did not improve the stages completed in the first trial, the total errors, and the total errors adjusted in the three-shape step of PAL (P > 0.05). MPH also improved all aspects of pattern recognition memory (PRM) (P < 0.05) and the mean correct latency of spatial recognition memory (SRM) (P < 0.05). However, MPH had no effect on delayed matching to sample (DMS) (P > 0.05). Conclusions: MPH improved performance on the PAL, PRM, and SRM visual evaluating tests of ADD patients. Nevertheless, the patients did not show any improvement in the DMS test. In comparison with previous studies, our results would suggest that MPH has similar effects on the visual memory of ADD and ADHD patients.