With the CrO3−phenylalanine complex as a precursor, pyrolysis was successfully used to create a rhombohedral green chromium oxide (Cr2O3-NP) nanostructure. As a clean process, CrO3 oxide and phenylalanine amino acid were subjected to solid–solid grinding for 1 h to create the CrO3−phenylalanine precursor. After characterization by infrared spectroscopy and microanalysis, the solid precursor compound was annealed for 3 h in static air at 600 ℃ in a muffle furnace. FT-IR spectroscopy, Raman laser spectroscopy, SEM, energy-dispersive X-ray spectroscopy (EDX), TEM, and X-ray powder diffraction (XRD) were all used to thoroughly characterize the resulting Cr2O3-NP. The existence of crystalline Cr2O3 is evident from the Fourier-transform infrared (FTIR) peak characteristic vibrations of Cr−O and two characteristic peaks at 646 and 568 cm−1 that are ascribed to Cr−O stretching modes, according to the results of spectral analysis. Since no distinctive impurity peaks were found, the FT-IR and XRD data demonstrated that the Cr2O3-NPs are pure and have an excellent crystalline structure. A UV–Vis spectrophotometer was used to quantify the energy band gap (4.80 eV) of the chromium (III) oxide nanostructures. A significant amount of nanostructure with an average crystal size of 5–7 nm was discovered using TEM and picture data, proving that this synthesis approach is an effective way to create Cr2O3 nanoparticles.