Being relatively volatile components of a commercial gasoline, hydrocarbons whose carbon number ranges from four to six, C4 to C6, were effectively removed by ultrasonic atomization. The ultrasonic frequency was 2.4 MHz, and the voltage applied to the oscillating unit was 24 V. More than 60% of C4 and C5 hydrocarbons were removed during 900 s of operation. In regard to the energy requirement for the separation, ultrasonic atomization needs only about half the energy required for evaporation. This finding is interpreted as a result of the phase change of liquids; the input energy was effectively utilized for the removal of light hydrocarbons. Operation at ambient temperature is advantageous for making use of a difference in vapor pressure among hydrocarbons.