Green synthesis of nanoparticles using plants has become a promising substitute for conventional chemical synthesis methods. This study aimed to produce chromium oxide nanoparticles (Cr2O3NPs) utilising lemon juice extract. The production of Cr2O3NPs was characterised using field emission scanning electron microscopy, transmission, X-ray diffraction, electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared, and ultraviolet–visible spectroscopy. The anticancer activity of Cr2O3NPs was determined against lung cancer cell line A549. The antioxidant activity was investigated in the ascorbic acid system. The antibacterial activity of the green synthesised nanoparticles was evaluated against two different bacterial strains, Streptococcus mutans and Escherichia coli. The anticancer activity of synthesised Cr2O3NPs at (6.25, 12.5, 25, 50, and 100) μg/mL against A549 cancer cells was substantial, with more than 70 % of cells cytotoxicity. While, Cr2O3NPs at (55, 62.8, 73.3, 88, and 110) μg/mL as antioxidant agents ascorbic acid system increases, the percentage of the inhibitor capacity by 29.5 %, 30.7 %, 34.5 %, 38.2 %, and 40.4 %, respectively. Finally, Cr2O3NPs at 100 μg/mL exhibit superior antibacterial activity against both Gram-negative bacteria within an inhibition range of 21 and 22 mm respectively.