This paper is to investigate the effect of altitude on Jet A's flash point using the experimental method. Firstly, the vapor pressure of four fuels is measured by saturated steam pressure tester with ND-1 pressure sensor in the low-pressure environment under nine different temperatures, and the results show that the Clausius–Clapeyron relationship between vapor pressure and temperature is applicable to the multicomponent mixture. Secondly, the BS-1 closed bomb apparatus is used to measure the oil samples, and the hypobaric chamber is applied to change the environment pressure from 55to 101.3 kPa. The flash point is found to decrease nonlinearly with the altitude increasing on the basis of the notion of a critical value of fuel–air mass ratio equals to 0.065 at the minimum flammability limit. Only when the atmospheric pressure approximates normal atmosphere does the flash point decrease linearly with the increase in altitude. This discovery agrees well with J.E. Shepherd's research. Thence, the experiment results provide scientific data for the safety of aircraft tank and benefit fire protection, such as inflammable liquid transport, storage, and so on, in oil pipeline management. Copyright © 2012 John Wiley & Sons, Ltd.