In order to improve biocompatibility and cell growth, poly-gamma-glutamic acid (gamma-PGA) was used as an additive, and a series of gamma-PGA/hydroxyapatite (gamma-PGA/HAp) nanocomposites were prepared. Then the morphology, water uptake and retention abilities, in vitro degradation properties in the simulated medium, and cytotoxicity of these gamma-PGA/HAp nanocomposites were investigated. The results show that the gamma-PGA/HAp nanocomposites have homogenous nano-sized grains, hydrophilicity, biocompatibility, and controlled in vitro degradation, suggesting that the gamma-PGA/HAp nanocomposites are novel nanostructure composites with great potential application in the field of bone tissue engineering.