In this study, fibrous nano-hydroxyapatite (HA, Ca10(PO4)6(OH)2) was synthesized directly via a hydrothermal method with additive-free. By adjusting the hydrothermal reaction time, HA samples with varying purity levels were obtained using the different reaction time. When the hydrothermal time was short, the samples exhibited diffraction peaks corresponding to HA standard peaks (JCDPS NO.09-0432), along with minor impurity peaks attributed to DCPA (Ca–HPO₄) and OCP (Ca8H2(PO4)6·5H2O). Relatively pure HA samples were fabricated when hydrothermal times exceeding 12 h. Furthermore, the intensity ratio of the (300) to (211) crystal plane diffraction peaks (I300/I211) reflects the preferential growth orientation of the crystallites. When the hydrothermal time increased from 6 to 18 h, the I300/I211 ratio of the samples continuously increased and consistently exceeded the theoretical value for standard HA peaks (0.61). This indicates preferential growth of the sample crystallites along the c-axis direction. For a hydrothermal time of 12 h, the fibers had a diameter of approximately 20 nm and an aspect ratio greater than 100. Adsorption experiments demonstrated that the sample achieved a copper ion adsorption rate exceeding 88%, under conditions ofa Cu(II) concentration of 100 mg/L and a solid-to-liquid ratio of 1:200. Besides of a large specific surface area, the fibrous structure of HA may also induce lattice strain and increase Ca2+ site vacancies, thereby enhancing the adsorption performance of HA. The prepared HA nanofibers exhibit excellent copper ion removal capability and have the potential to serve as effective adsorbents for heavy metal ions.