In this research, nanoparticle of lanthanum oxide (a) has been synthesized in a co-precipitation method and its ability to be antibacterial has been studied. The La2O3 crystalline nanoparticle (a), prepared at a nominal temperature of 673 K for 4 hours. The samples were identified using FT-IR, XRD, VSM, SEM, and EDX methods. Using the infrared spectroscope (FT-IR), the covalent bonding of La2O3 in the sample is confirmed. X-ray diffraction (XRD) shows that the single-phase sample has a hexagonal structure with average particle size 69 nm. Also, the size of the particles seen in the SEM images corresponds to each other. Using the Vibration Sample Magnetometer (VSM), the magnetic properties of the nanoparticle (a) were studied and result shows that nanoparticle has paramagnetic behavior.The antibacterial effects were also examined in vitro against standard bacterial strains, the Gram-positive Staphylococcus aureus; S. aureus ATCC 25923 and Enterococcus faecalis; Enter_faeca ATCC 29212, and also the Gram-negative Escherichia coli; E. coli ATCC 25922 and Pseudomonas aeruginosa; P. aeruginosa ATCC 27853. Using these strains, the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and inhibition zones (IZ) were obtained. Antibacterial activities of lanthanum oxide nanoparticle are more than agents lanthanum salts.