The propagation behavior of chemical waves in the Belousov-Zhabotinsky reaction was examined experimentally for the first time under microgravity conditions. This study was motivated by the work of Kondepudi and Prigogine (1981), who pointed out theoretically that a diffusion reaction system with nonlinear and nonequilibrium characteristics may receive a great amplification of the subtle effect of gravity on elementary reactions. In the present study, the free-fall facility at the Japan Microgravity Center in Hokkaido (JAMIC) was utilized to maintain a quality of 10(-5) g for about 10 s. To prevent convection due to surface tension, a thin planar vessel closed to air was used in both normal and microgravity runs. Concentric patterns induced spontaneously in the vessel fixed in the vertical position were elongated downward and shortened upward under normal gravity. Under microgravity, however, propagation speed was almost the same in traveling directions. To discuss the effect of convection, propagating speed in gel matrix was also observed in similar experiments under microgravity conditions, but no apparent influence was revealed.