Abstract: Objective: To establish a sensitive RP-HPLC method for determining the content of the active ingredient-melatonin in the different species of aloes and their tissues. Method: To make Making use of Symmetry C18 150 mm×4.6 mm, 5.0 μm) as column, with the flow of carbinol: water in the ratio 1:1, at the flow rate 1.0 ml/min. The inspected wavelength is 223 nm with sensitivity degree 2.00 AUFS. Result: The linear range for melatonin is perfect within 2.0～200.0 pg/ml (r=0.9892) with the average recovery(n = 6) 98.8% and RSD 1.13%. The method is simple and easy for determinfim of the melatonin content in aloe. The melatonin content varies in different species of aloes and their different tissues, and the content in the flower is higher than that in the leaf of aloe. The content of melatonin in Aloe vera L. is the highest.

Key words: RP-HPLC, aloe, melatonin