The alleviating effects of calcium compounds on fruit puffing were investigated in satsuma mandarin. The ultrastructural changes in the subepidermal cell walls of puffy fruits and the inhibiting strategies of calcium against these changes were also observed under transmission electron microscope. Although puffing occurred in both treated and non-treated fruits under certain environmental conditions, pre-harvest applications of CS-2H (CaSO₄·2H₂O, CaCl₂) and CS-1B (CaCO₃ microcrystal suspension) significantly reduced it and with the exception of peel puffing these chemicals did not affect other fruit characteristics. The subepidermal cells of non-treated puffy fruits had bigger intercellular spaces in the cell corners and schizogenous intercellular spaces between adjacent walls. Occasionally, cell corners and abutting walls did not possess these spaces, but the disintegration of middle lamella therein was distinct. The disintegration caused loosening of the intercellular connection and swelling of walls. The sporadic destruction of the cell wall was also found near the plasma membrane. The fibrillar materials of loose cell walls separated distinctly in the longitudinal direction ; this separation was crosswise near the plasma membrane. In a few cases, the middle lamella and its adjoining walls had disintegrated. The application of calcium compound (CS-2H) prevented these ultrastructural disorders so that intercellular spaces remained small, schizogenous intercellular spaces did not develop, and the dissolution of middle lamella was checked considerably. The cell corners retained their middle lamella or sometimes developed small intercellular spaces. The fibrillar materials in the cell walls were compact and their destruction was not evident. Cell wall swelling was rarely observed, and cellular separation was not found.