Much of the plastic film house soils in the southern part of the Korean peninsula are managed using a rotation system which rotates between non-submerged and paddy soils to prevent salt accumulation. High amounts of salts including phosphate is released during the rotation, and then became an important source of water euthrophication. To reduce phosphorous release from the soil during the rotation, we selected a industrial by-products, oyster shell meal, which has high content of calcium and then might convert water-soluble phosphorus to less soluble forms, as a soil amendment. To examine the mechanisms by which oyster shell meal increases the sorption of fertilizer-P in soils, either oyster shell meal or soil was shaken for 24 h with KH2PO4 solutions in 10 mM CaCl2. With oyster shell meal, grinding increased sorption by a factor of about 3, and increase in pH from 5.6 to 7.5 greatly increased sorption. Scanning electron micrographs (SEM) and EDX quantitative analysis showed that small crystals of oyster shell meal disappeared and roughly spherical particles of DiCalcium Phosphate (DCPD) were formed. Analysis of equilibrium solutions showed, using GEOCHEM, that Octa-Calcium Phosphate (OCP) coated the DCPD. SEM and EDX could not be used in the soil matrix, but solubility analysis again showed that solutions were close to equilibrium with OCP. Oyster shell meal increased sorption by being a source of readily available Ca2+, and therefore might be effective on reducing phosphorus release from phosphorus accumulated soil.