Abstract: Gravitropism is an important physiological response and an essential mechanism for plants to maintain the normal growth and development on earth. In the life cycle of higher plants, seed development is a key process, but whether gravity can affect the development of seeds has not been confirmed. In this study, the development of siliques and seeds of Arabidopsis under the 3D clinostat rotated condition was analyzed to examine whether seed development including formation of embryos and the activities of metabolism is affected by the altered gravity condition. Our results showed that in the 3D clinostat rotated treated Arabidopsis plants, the morphology of siliques showed an irregular curvature, and the cell division and elongation of suspensor were inhibited. The content of soluble carbohydrates and starch in the young and mature seeds obviously increased, while the content of salt soluble protein decreased. In addition, developing seeds at globular stage are most sensitive to the 3D clinostat rotated treatment with the inhibition of cell division and elongation of the suspensors. Suspensors are important for the transportation of nutrients into embryos and abnormal development of suspensor under the clinostat rotation condition might cause seed abortion.