Copper oxide (CuO), titanium oxide (TiO 2), and Cu-doped TiO 2 nanoparticles have been synthesized by pyrolysis of their corresponding precursors initially prepared by precipitation in aqueous solution using A. carambola fruit juice as a natural source of the precipitating agent (oxalate). The precursors were synthesized and characterized by FTIR, TGA, and PXRD. The results revealed that the precursors obtained were CuC 2O 4, TiO 2(OH −) 2C 2O 4, copper-doped titanium hydroxyl oxalate, and copper titanium hydroxyl oxalate. Complete decomposition for the as-prepared precursors containing titanium ions occurs at 600°C while impurity free copper oxalate decomposed at 450°C. The as-prepared precursors were decomposed and calcined at 600°C for 4 hours and the calcination products were characterized by XRD, SEM, and EDX. The results revealed the decomposition products to correspond to CuO, TiO 2, Cu 0.131Ti 0.869O 2, and CuO/TiO 2.