The optical levitation of a liquid droplet in the gas phase was investigated under a time-dependent change in the gravitational acceleration in an airplane following a specific flight profile. Through multiple trials under a linear increase in effective gravitational acceleration, we performed an experiment on the optical trapping of a droplet from 0.3g(0) to 0.9g(0), where g(0) = 9.8 m/s(2). During this change in the effective gravitational acceleration, the trapping position of a droplet with a radius of 14 mu m was found to be lowered by ca. 100 mu m. The essential feature of the change in the trapping position was reproduced by a theoretical calculation under the framework of ray optics. To the best of our knowledge, this study is the first to report on optical levitation under a time-dependent gravitational change. (c) 2005 Elsevier B.V. All rights reserved.