A strong gravitational field resulted in the gravity-induced diffusion (sedimentation) of isotope atoms in monoatomic solid Se. The layer crystalline morphology consisting of three zones of the fine-grained crystals, the long crystals and feather-shaped crystals grown parallel to gravity direction appeared in the specimen ultracentrifuged at (0.8–1)×10⁶ G and at 190°C. Change in the concentration ratio ⁸²Se/⁷⁶Se of >0.8% was observed in the grown crystalline region. These results show an evidence for the sedimentation of substitutional atoms in solids via self-diffusion, and suggest the possibility of application to the control of impurity and crystalline states as well as to isotope separation.