Abstract: Despite the fact that leaves of Vitex doniana has been in use for many decades in the treatment of many illnesses, little is known about its effect on serum electrolytes balance in mammals. This study sought to determined the effects of its aqueous leaves extract on serum electrolytes (sodium, potassium, chloride and bicarbonate ions) using standard laboratory methods, following 4 weeks oral administration to 30 albino rats at varied doses (100, 150 200 mg kg-1) with 10 albino rats as control group. The values of serum sodium, potassium, chloride and bicarbonate ions for the control group were 170±.00, 5.3±0.16, 130±2.00, 30±2.00 mMol L-1, respectively. However, significant increase (p<0.05) in serum chloride and bicarbonate ions was found at 100, 150 and 200 mg kg-1 and potassium ion at 150 and 200 mg kg-1, where as sodium ion at only 150 mg kg-1. It can be inferred that Vitex doniana leaves extract at dose of 150-200 mg kg-1 could be toxic. Therefore, like any other drug, it should be taken at a therapeutic dose to be determined, since it has been found to increase electrolytes level and may help in replenishing loses.