The aim of this study was to design and evaluate nano-hardystonite/polyamide 66 composites with close mechanical properties to the trabecular bone to prevent the stress shielding phenomenon for bone tissue engineering applications. This composite can be used as an intervertebral fusion cage to perform spinal fusion between vertebrae in the lumbar spine. The pure nano-hardystonite powder was fabricated by combustion method at 900 °C following by 5 h ball mill. The nano-hardystonite/Polyamide 66 and nano-hydroxyapatite/Polyamide 66 cage were prepared by injection molding method to compare the mechanical and biological properties. In this end, the X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilized to characterize the prepared powder and cage samples. Based on the results, the addition of 30% nano-hardystonite improved both mechanical and bioactivity properties. The optimum hardystonite/PA66 samples revealed the compressive strength and elastic modulus of 69.19 ± 0.89 MPa and 2.56 ± 0.5 GPa, respectively, compared to 53.45 ± 1.2 MPa and 3.45 ± 0.3 GPa in hydroxyapatite/PA66 sample, respectively. In addition, observation of the superior apatite formation ability of hardystonite/PA66 compared to hydroxyapatite/PA66 indicated that it can be used as a spinal vertebrae replacement material.