Two crystals of Bi2Se0.21Te2.79 doped with 0.08 wt% TeI4 were grown by zone melting on the Foton-M3 spacecraft of Russia and the ground in 2007, respectively. The chemical composition, structure and thermoelectric properties of the space and ground crystals grown were evaluated by EPMA, XRD and thermoelectric measurements including Seebeck coefficient, electrical conductivity and thermal conductivity. The compositions of the space crystal grown along growth direction were more homogeneous than that of the ground crystal grown. The crystallization of space crystal grown was obviously improved. The maximum ZT value of space crystal reached 1.14 at 300 K, which was higher about 29% than that of ground crystal at room temperature. These results imply that the composition homogeneity and crystallization of Bi2Se0.21Te2.79 crystal can be improved under microgravity conditions, which is helpful for enhancing thermoelectric figure of merit of Bi2Te3-base materials.