Background: Recently, the use of synthetic bone graft substitutes has garnered attention and become more popular than traditional methods for reconstructing osseous defects in the fields of orthopedics and maxillofacial surgery. Commercially available hydroxyapatites (HAs) have been widely reported to be effective bone graft substitutes. Unfortunately, they are expensive to produce. Thus, there is a need to develop methods of producing HA bone graft substitutes from inexpensive sources. Objectives: To synthesize nanocrystalline HA using recycled eggshell and trimethyl phosphate. Until date, several phosphate solutions have been utilized for this purpose. However, this is for the first time to the best of our knowledge that trimethyl phosphate is used as a source of phosphate to synthesize eggshell-derived HA. Methods: To produce HA, calcined hen’s eggshell was used as a source of calcium, and trimethyl phosphate was used as a source of phosphate in a sol-gel method at a controlled temperature. The results were estimated using scanning electron microscopy (SEM) observantion to evaluate surface morphology, X-ray diffraction (XRD) to analyze phase composition, and transmission electron microscopy (TEM) to evaluate the shape and size of prepared HA. Micro-chemical analysis was conducted using energy-dispersive X-ray spectroscopy (EDX). Fourier transform infrared spectroscopy (FTIR) was employed to identify the functional groups of the prepared HA. Results: XRD evaluation showed that high-purity synthetic HA powder was obtained. The results of the SEM, XRD, TEM, EDX, and FTIR analyses demonstrated that the synthesis yielded nanostructured HA. Conclusions: A complete synthesis of nanocrystalline HA was obtained by using trimethyl phosphate and eggshells in a sol-gel method at a controlled temperature. A spherical particle morphology and particle size ranged 19 - 41 nm were achieved. Eggshell waste material is inexpensive and can be considered a viable choice for high-volume HA powder production, based on the present results.