An unconventional but robust route to fabricate highly pure α-Al₂O₃ colloidal nanocrystals with tunable surface chemistry and dimensions was introduced based on semi-aromatic polyamide (PA6Py) with pyridine rings as a functional matrix. The surface ligands of α-Al₂O₃ nanocrystals can be tuned by choosing different carboxyl-terminated polymers (e.g., PS and PEO).