A new eco-friendly method, safe and harmless, for lanthanum oxide nanoparticles (La2O3 NPs) using Physalis angulata leaf extract (PALE) has been successfully synthesized. La2O3 NPs was prepared by sol-gel technique using La(NO3)3.6H2O precursor and PALE biomaterial. The secondary metabolites in PALE act as weak base source and stabilizing agent in La2O3 NPs formation. Identification of secondary metabolites was analyzed by phytochemical test. Characterization of La2O3 NPs functional groups was conducted by Fourier transform infrared (FTIR) spectroscopy. FTIR spectrum result shows the specific vibrations of La-O at wavenumbers of 400 and 454 cm-1. The crystallinity of La2O3 NPs was analyzed by X-ray diffraction (XRD). The morphology and element composition of La2O3 NPs were investigated by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). The shape and particle size of La2O3 NPs indicated by transmission electron microscopy (TEM) image were found in spherical shape with size in the range of 25-50 nm. UV-Vis-diffuse reflectance spectroscopy (UV-Vis-DRS) was used to determine band gap value of La2O3 NPs. In this study, the band gap value of La2O3 NPs was 5.39 eV.