Bacterial diseases are among the most significant challenges in the aquaculture, and the widespread use of antibiotics to control infections has led to the drug resistance. So, the search for natural and safe alternatives, such as plant extracts, is essential. The aim of the present study was to evaluate the antibacterial activity of the aqueous extract of sumac (Rhus coriaria) and Iranian mountain leek (Allium iranicum), as well as to investigate the effect of their combination against three important aquatic pathogens: Streptococcus iniae, Lactococcus garvieae, and Aeromonas hydrophila. Aqueous plant extracts were prepared using the cold maceration method (1:20 w/v ratio, 48 hours; dry extract yield: sumac ~10%, Iranian mountain leek ~7%). Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) assays were performed using the broth microdilution method in Nutrient Broth, following CLSI protocols (with modifications for compatibility). The results were analyzed using SPSS software. The results showed that sumac extract had stronger antibacterial activity compared to the Iranian mountain leek extract and exhibited the lowest MIC values, particularly against S. iniae. The combination of the extracts improved the antimicrobial activity of the Iranian mountain leek but did not surpass the effect of sumac extract alone. Analysis of the MBC/MIC ratio indicated that most treatments had a bactericidal effect, although sumac extract showed a bacteriostatic effect against Gram-positive bacteria. In general, the results of this study demonstrate that sumac and its combination with Iranian mountain leek can be considered as promising natural alternatives for controlling bacterial infections in aquaculture.