Physical property of plant has to be described on the basis of cellular structure. However, even deformation of a single cell has not been confirmed experimentally. In this study, deformation of single cell is analysed. Following four conditions are established for plant cell: l) the cell wall can be treated as isotropic elastic membrane, 2) the cell fluid is incompressible, 3) effect due to exosmosis during compression is neglected and 4) the deformation due to mass of cell fluid is ignored. Under these conditions, single cell under compression is supposed to change from sphere to ellipsoid of revolution and can be modelled with rubber ball filled with water. Then relation among volume, stress, strain and pressure were analysed as ellipsoide. Parameters of ellipsoid were also identified in experiment using rubber ball. Calculated value were fitted to measured value. The results, confirmed that model cell was changed from sphere to ellipsoid of revolution.