The present work demonstrates the production of chlorapatite (ClAp) through thermal decomposition of chemically treated fish scales, originating from an Amazon fish species (Arapaima gigas). The scales were treated with hydrochloric acid (HCl) solution for deproteinization. Afterwards, the solution was neutralized by sodium hydroxide (NaOH) treatment to obtain an apatite-rich slurry. The heat treatment was carried out at different temperatures including 600 °C, 800 °C, and 1000 °C. The powders obtained were characterized through X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM). The XRD analysis and FTIR spectra confirmed the incorporation of chlorine into the apatite structure. The FTIR results showed absorption bands relative to the OH-, PO43- functional groups which are a characteristic of chlorapatite; moreover, the intensity of the OH-Cl elongation could be observed. Chlorapatite Ca5(PO4)3Cl, NaCl, and NaCaPO4 phases were identified, achieving up to 87.4 wt% for ClAp. From the SEM observations, the ClAp obtained consisted of slightly larger grains and more crystalline with increasing temperature with observed grains ranging in sizes between 1 and 5 μm and 84.27% crystallinity for the ClAp1000 sample. The ClAp and NaCaPO4 can be used in electronics as a phosphor material due to the fact of its luminescence and biomedical applications.