Atomoxetine is a non-stimulant selective noradrenergic reuptake inhibitor, with FDA approval for the treatment of attention deficit hyperactivity disorder (ADHD). It is considered as a safe drug in terms of drug abuse. Atomoxetine is a commonly used drug in children and adolescents and leukopenia is a rare side effect of atomoxetine. In this case, we discuss a 11 year-old-male patient using atomoxetine without a history of hematologic disorders. Leukopenia was occurred in therapeutic doses of atomoxetine After discontinuation of atomoxetine treatment improved leukopenia This finding suggests us to be aware of potential leukopenia side effect of atomoxetine.