Single-droplet evaporation of fuel at high pressures and high temperatures has been studied experimentally under microgravity conditions. Suspended n-heptane droplets were employed in the experiments at pressures in the range of 0.1∼5.0 MPa, and temperatures varying from 400 to 800 K. Temporal variations of the droplet diameter were measured for subcritical environments with a computer-aided image analysis system. Microgravity conditions were used to prevent natural convection that makes phenomena complicated, and realized by using 5 m and 110 m drop towers and parabolic flights. It was observed that dense fuel vapor accumulates around a droplet and that the droplet surface becomes obscure in high-pressure and high-temperature environments. At ambient pressures below the critical pressure of the fuel, the slope of the variations of the squared nondimensional droplet diameter with the corrected time initially increases but later becomes constant. At pressure of 5.0 MPa and temperatures below the critical temperature, it becomes gentler in the latter half of the droplet lifetime.