ABSTRACT Synergy refers to the combination and interaction of two or more agents which produces a result that is greater than the sum of their individual effects. Hence, the synergistic assessment of the effects of Sida acuta & Citrus aurantifolia, Sida acuta & Dioscorea bulbifera and Citrus aurantifolia & Dioscorea bulbifera combined extracts on selected bacteria (Escherichia coli0157:H7, Salmonella typhymurium and Vibrio cholerae) were investigated. The study area was Omuanwa in Ikwerre Local Government Area of Rivers State, Nigeria were the plants were collected. The test organisms were identified by polymerase chain reaction technique, while the antimicrobial effects of the combined plant extracts were examined against the different bacterial species by agar well diffusion method and sensitivity interpreted in accordance with the Clinical and Laboratory Standard Institute. Phytochemicals extracted were Flavonoids, Cardiac Glycosides, Tannin, Phenols, Alkaloids, Steroids, Terpenoid and Saponins, however, the concentrations of phytochemicals extracted by ethanol and aqueous showed statistical significant difference of p<0.05. The organisms were more sensitive to Citrus aurantifolia & Sida acuta with 91.7%, followed by Citrus aurantifolia & Dioscorea bulbifera and Sida acuta & Dioscorea bulbifera with equal sensitivity of 75.0%, also evident in the mean zones of inhibitions, as the highest mean of 15.500mm was observed in Citrus aurantifolia & Sida acuta against all test organisms followed by Citrus aurantifolia & Dioscorea bulbifera (12.667mm) and Sida acuta & Dioscorea bulbifera (12.417mm). Escherichia coli0157:H7 was most sensitive to Sida acuta & Dioscorea bulbifera, Salmonella typhimurium was most sensitive to Citrus aurantifolia & Sida acuta, while Vibrio cholerae was most sensitive to Citrus aurantifolia & Sida acuta. Considering different mean concentrations of combined extracts of 100%, 75%, 50% and 25% against the test organisms, the mean zone of inhibitions was in the order of increasing concentrations, the higher the concentrations the higher their zones of inhibition. The ability of the combined extracts to have shown cleared zone of inhibitions indicates synergism. Keywords: Sida acuta & Citrus aurantifolia, Sida acuta & Dioscorea bulbifera, Citrus aurantifolia & Dioscorea bulbifera, Escherichia coli0157:H7, Salmonella typhymurium, Vibrio cholerae. Synergy, Combined Extracts.