The abuse of synthetic antibiotics is one of the leading causes of the emergence of antibiotic-resistant microorganisms that have become the primary health concern. To overcome this resistance and counteract all the side effects of synthetic drugs, attention was diverted towards natural resources for developing antimicrobial substances. This study tests the effect of carrageenan isolated from Kappaphycus alvarezii on pathogenic bacteria. Carrageenan is a natural bioactive compound extracted from red algae. Carrageenan was extracted from K. alvarezii using hot water extraction. The antimicrobial property of carrageenan was tested using the Minimum Inhibitory Concentration and the bacterial cell growth rate. Moreover, a commercial antibacterial hand wash and anti-acne toner were used as comparative agents. Firstly, a series of concentrations were used, from 25 µg/mL to 10 mg/mL. The results showed no antimicrobial activity of carrageenan extracted from K. alvarezii using ethanol toward the strains used in this study, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Staphylococcus aureus. However, the carrageenan extracted exhibited a growth-boosting effect over the microorganisms used. Thus, further studies can be carried out using different carrageenan extract methods for K. alvarezii to ensure that anti-microbial compounds from K. alvarezii can be extracted during the carrageenan extraction.