Photocatalytic oxidation (PCO) using fluorescent light was used to disinfect two marine bacteria: Alteromonas alvinellae and Photobacterium phosphoreum. Results showed that P. phosphoreum exhibited a lower susceptibility towards PCO than A. alvinellae, which was related to their fatty acid profiles and levels of superoxide dismutase (SOD) and catalase (CAT). Results also revealed that CAT and SOD levels would be triggered by PCO reaction. In addition, PCO disinfection efficiency could be enhanced by acidic pH levels and increased temperatures, while different growth phases demonstrated diverse effects to the studied bacteria, probably due to their morphological difference or change in physiological state. Lastly intracellular leakage of potassium ion (K(+)), in line with the loss of cell viability, was observed during PCO. Mineralization of bacteria by PCO was monitored by total organic carbon analysis. From the regrowth study, the tested strains failed to reactivate within 96h after PCO treatment, indicating PCO caused irreversible bacterial inactivation.