n-Butyl benzoate is proposed as a new medium for the falling drop method of determination of deuterium oxide in a sample of dilute heavy water.It is suitable for analysis in the concentration range of 0-10.5 mol% D₂O at working temperatures 22-33.5℃.A mixed medium composed of n-butyl and iso-butyl benzoate in about 1:1 ratio can be applied to analysis for 0-7 mol% D₂O at working temperatures 21.5-26.5℃.iso-Butyl benzoate can be used at 20.5℃ for analysing 0-4 mol% D₂O.Calibration curves for these media are shown in Fig.9 and 10* (in Chinese text).The relative error of determination is about 0.1%.