The methanol extract of Kappaphycus alvarezii was evaluated for antibacterial activity and against the human clinical isolated pathogens of Staphylococcus aureus, Bacillus cereus, Pseudomons aeroginosa, Escherichia coli, Proteus vulgaris and Bacillus subtilis. The phytochemical analysis showed the presence of alkaloids, saponin, phenols, terpenoids, coumarins, protein, carbohydrates, flavonoids, tannins and absence of steroids, glycosides and anthraquinone. Kappaphycus alvarezii possesses significant antibacterial activity and in future the methanol extract may pave the way for designing the new drugs for controlling bacterial diseases.