We investigated the effect of hydroxyapatite(HAp) nanoparticle content on the characteristics of HAp/chitosan composite film containing $50 wt.\%$ citric acid based on HAp content. Several compositions of HAp/chitosan composite films were prepared by co-precipitation and solvent casting method. According to turbidity measurements, HAp particles whose diameter were generally less than 500nm were homogeneously dispersed in chitosan matrix and all the films were transparent. HAp/chitosan composite films were characterized by X-ray diffractometer(XRD) and differential scanning calorimetry(DSC). The degree of swelling decreased with decreasing chitosan content. Tensile strength and modulus revealed that HAp/chitosan films became rigid and brittle with increasing HAp content. The increase of surface energy was due to the increasing interaction among the HAp nanoparticle, citric acid, and chitosan.