Protein loading on apatite hydrogel cake and its solubility was studied. A mixture of di-sodium hydrogen phosphate dodeca-hydrate and calcium chloride di-hydrate was dissolved in water, and kept at room temperature for 2 weeks in air or N2 atmosphere to make apatite hydrogel. The obtained apatite hydrogel contains carbonate ions, and its carbonate content strongly affect the aggregation of particles. With maturation period, the particle size of apatite hydrogel decreased in air, but increased in N2 atmosphere. The quantity of loaded Cytochrome C in apatite hydrogel formed in air was 0.490 wt%, while that in apatite hydrogel formed under N2 atmosphere was 0.305 wt%. But the quantity of loaded albumin in apatite hydrogel formed in air was less than that in apatite hydrogel formed under N2 atmosphere. The difference may be due to the relationship between isoelectric point of protein and apatite hydrogel. The apatite hydrogel containing protein was dried for 4 days in air at 40 % of relative humidity to make cakes, and the cakes were immersed in pure water or PBS solution. The dried specimen slowly dissolves in aqueous solution, and the decrease in weight of apatite cake prepared from hydrogel formed in air was larger than that from hydrogel formed under N2 atmosphere compared to the dissolved apatite, the released protein was less, which may be associated with recrystallization of the apatite hydrogel.