Abstract: Objective: To set up a model and study the effect of gelatin, as organic matrix, on the process of biomineralization. Method: 30mM calcium solution and 5mM phosphate solution were added into the mineralization device respectively. Gelatin was injected into the reaction space between the cation-exchange membrane and dialysis membrane. The cation-exchange membranes were gained after 7 and 21days and the sediments on the membranes were prepared for SEM, XRD and EDX. Results: Crystals in the sediment become aciform or prismatical as the reaction time being prolonged. When 10% gelatin was added into the reaction space, the crystals became fasciculate. And the Ca/P proportion of the crystals raised when the gelatin’s concentration was changed to 20%, which meant the transformation of amorphous calcium phosphate to hydroxyapatite. Dentin-like sediments were formed on the ion-selective membrane with 20% gelatin added into the reaction space after 21 days. The crystals appeared typical hexagonal prism or hexagonal cone of around 100nm in diameter and 2um in height as they grew along c-axis direction. Analysis by energy dispersive x-ray diffraction showed that these precipitates were HA. Conclusions: Gelatin can promote the process of biomineralization and the transformation from amorphous calcium phosphate to hydroxyapatite.