The marine seaweeds are one of the vital living resources. The present study is focused on antibacterial and larvicidal activity of marine red algae Kappaphycus alverazii. The antibacterial activity of methanol extract was analysed for in vitro antibacterial activity against selected test pathogens Escherichia coli, Staphylococcus aureus, Bacillus subtilis, Klebsiella pneumonia and Bacillus cereus. The methanol extract of red algae Kappaphycus alverazii showed maximum zone of inhibition (32 ± 3.1) against test pathogen of Escherichia coli. The in vitro mosquito larvicidal activity was performed with different concentrations using Anopheles stephensi. Methanol extract exhibited high mortality rate effective against Anopheles stephensi after 24 hours of exposure. © 2020 World Research Association. All rights reserved.