Potassium bromate (KBrO3) is widely used as a food additive and is a major water disinfection by-product. The present study reports the side effects of KBrO3 administration in Swiss mice. Animals were randomly divided into three groups: control, low dose KBrO3 (100 mg/kg/day) and high dose KBrO3 (200 mg/kg/day) groups. Administration of KBrO3 led to decreased white blood corpuscles (WBCs), red blood corpuscles (RBCs) and platelets count in the animals of both the high and the low dose groups.