Recent advancements in the field of natural therapeutics have consistently highlighted the potent antibacterial properties of medicinal plants, unveiling new pathways in the fight against bacterial pathogens. This emerging knowledge is particularly relevant in aquaculture sector , where the search for effective, natural, and sustainable treatments against fish pathogens is importance. Within this context, the aim of this research is to evaluates the antimicrobial effectiveness of methanolic extracts from the Gelenggang plant ( Cassia alata ), focusing on its action against the Gram-negative bacteria Vibrio alginolyticus and Edwardsiella ictaluri , both of which pose notable challenges in aquaculture. A gar disc diffusion method for an initial evaluation of antibacterial activity was carried out . This was followed by determining the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of the extracts. The extracts exhibited antibacterial activities against tested microorganisms. Methanolic Gelenggang extract showed significant antibacterial activity against E. ictaluri , while a low inhibitory effect on V. alginolyticus was observed. The methanolic extracts of Gelenggang with different concentrations showed antibacterial effects against E. ictaluri with diameter zone of inhibition ranging from 14 mm to 8 mm . Through MIC and MBC determination, E. ictaluri also appears to be the most sensitive to the methanolic extract of Gelenggang with a MIC value at 200 mg/ml concentration . However, for V. alginolyticus , no MIC and MBC value is shown. According to these findings, methanolic gelenggang extract is inefficient for treating bacterial infections in aquaculture because it has low efficacy in inhibiting the growth of bacteria V. alginolyticus and E. ictaluri compared to commercial antibiotic oxytetracycline.