Murphree stage efficiencies of minute components (n-propyl alcohol and iso-butyl alcohol) in ethanol aqueous solution were determined by using a 10-stage Oldershow type rectification column. By employing the azeotropic operation of ethanol-water systems, constant equilibrium ratios of the minute components were realized throughout all stages of the column to obtain the precise values of the Murphree Stage efficiencies. The following results were obtained; 1) Murphree stage efficiencies for both minute components were almost the same and decreased from 0.80 to 0.65 when decreasing the pressure from 101.3 to 12.7 kPa. 2) The same results were obtained for periodic and continuous reflux operations to confirm that the laboratory scale data obtained by periodic reflux would be applicable to industrial scale situations.