A psychophysical experiment was conducted to evaluate the interior design alternatives of a highspeed train. Preference of each design alternative was quantitatively measured by using the magnitude estimation technique. Subsequent analyses showed that (1) passenger seats should be able to be arranged in the moving direction of a train, (2) a variety of interior convenience facilities, especially, an audio facility, should be provided to enhance passenger comfort and (3) the design requirements suggested by young passengers could improve the overall preference level. In addition, guidelines for collecting, standardizing, and analyzing the data are suggested when the magnitude estimation technique is used. The use of psychophysical data is expected to be very useful when it is necessary to make engineering decisions based on quantitative preference data.