Background: The resistance of pathogenic bacteria against synthetic drugs led scientists to conduct research on medicinal plants. The present study investigated the antioxidant and antibacterial activity of the aqueous, methanol, and ethanol alcoholic extracts of the plant Citrus maxima Merr. (Syn. Citrus grandis) against some human pathogenic bacteria. Then, the presence of secondary metabolites was evaluated in vitro, including alkaloid, saponin, and tannin. Methods: The samples (i.e., root, stem, and seed) of C. maxima were collected at Babolsar, Mazandaran province, Iran. The agar well diffusion assay was used to determine antibacterial activity. In addition, several bacteria were applied based on the aim of the study, including Streptococcus pyogenes (PTCC- 1447), Bacillus subtilis (PTCC-1156), Bacillus cereus (PTCC-1247), Enterococcus faecalis (PTCC-1185), Micrococcus luteus (ATCC-10987), and Staphylococcus aureus (PTCC-1189). Further, some Gramnegative bacteria were used, encompassing Escherichia coli (ATCC-25922), Shigella boydi(-), Salmonella typhi (PTCC-1609), Pseudomonas aeruginosa (PTCC-1181), Enterobacter aerogenes (PTCC-1221), and Klebsiella pneumoniae (PTCC-1139). Next, the minimum inhibitory and bactericidal concentrations were determined by the serial dilution method. Furthermore, free radical activity was identified by 2,2-diphenyl-1-picrylhydrazyl. Moreover, the total phenolic and total flavonoid contents were conducted by Folin-Ciocalteu and aluminum chloride methods, respectively. Finally, the phytochemical compounds were investigated as well. Results: The highest sensitivity was observed on M. luteus against the root methanol extract. Additionally, the total phenolic content of root, seed, and leaf was determined as 98.22, 89.66, and 77.51 (mgGA/g), respectively. Similarly, the flavonoid content was determined as 3.52, 3.43, and 3.56 (mgQ/g), respectively. In addition, the IC50 of the root, seed, leaf, and ascorbic acid were calculated as 0.129
