Melatonin content in pharmaceutical products was quantitatively determined by capillary electrophoresis within 4 min. Sample preparation required the simple dissolution in water and filtration. An internal standard was used a linear relationship between melatonin concentration andR(melatonin corrected peak area/I.S. corrected area) was obtained, withr2>0.998. Separations were carried out in coated capillaries with a borate running buffer. The method showed an high precision with a RSD value for migration times of 0.3% for intra-day and 1.4% for inter-day measures (n=48). For theR parameter RSD was 2.9% and refers to seven consecutive runs of the same sample on the same day. Two commercially available pharmaceutical products containg melatonin were analyzed. The method offers an easy and accurate routine option.