Abstract: Altered gravity (microgravity and hypergravity) could affect many aspects of plants, such as growth, development, metabolism, ultrastructure, gene and protein expression. Ca²⁺ might play a role as a signal molecular in such graviresponses of plant. We supposed that the consequence of events occurring in plant cells under altered gravity were in the following order: gravisensing---changes in the cytoplasmic membrane surface tension---alterations in the physicochemical properties of the membrane---changes in membrane permeability, ion transport, membrane-bound enzyme activity etc--- Ca²⁺ signaling---metabolism rearrangements---physiological responses. Under altered gravity, the intracellular Ca²⁺ balance was redistributed and the increased cytosolic Ca²⁺ concentration was the key step of transforming altered gravity stimulation into intracellular Ca²⁺ signal. Ca²⁺ influx into the cytosol was via activation of Ca²⁺ selective ion channels and inhibition of Ca²⁺-ATPases. Following the increased cytosolic Ca²⁺ concentration, altered gravity induced a series of biological effects by regulating enzyme activity, with involvement of regulatory Ca²⁺ messenger system. This paper summarized the influences of altered gravity on plant intracellular Ca²⁺ balance and discussed the possible pathways of Ca²⁺ influx/efflux and Ca²⁺ signaling in plant cell biochemical regulation to altered gravity.