Eggshells (ES), are composed of inorganic and organic components that can be transformed into useful materials in the biomedical field such as hydroxyapatite (HAP). So far, many approaches have been developed to transform ES to HAP; most of them are two steps involving calcination at a high temperature and a chemical reaction step to form HAP. In this study, the potential to synthesize HAP from untreated chicken ES was investigated via a “one-pot” hydrothermal method. The reaction via the one-pot hydrothermal method was studied to simplify the synthesis of hydroxyapatite from untreated eggshells by varying the reaction time of the process. ES without sintering treatment was used for the HAP synthesis process and compared to that of the conventional treated ES after sintering at 1000 ℃ temperature. The structures and morphologies of HAP were analyzed by X-ray fluorescence spectrometer (XRF), X-ray Diffraction (XRD), Fourier Transform infrared (FTIR), and Scanning Electron Microscopy (SEM). The results showed that HAP presents in all samples with different crystalline sizes and morphologies. The presence of some other trace elements in the produced HAP from ES could play an important role in bone metabolism. The obtained HAP from the study showed promising results for use in biomedical applications.