Dental caries is a common disease caused by plaque biofilms, which are important pathogenic factors in many diseases. When hosts are overexposed to dietary sugars, pathogens such as Streptococcus mutans (S. mutans) and other cariogenic bacteria, metabolically assemble an extracellular matrix rich in exopolysaccharides to form a disease-causing biofilm, in which the microenvironment is characterized by regional hypoxia, low pH, and nutritional deprivation. Current antimicrobials with inadequate penetration and a lack of pathogens targeting the biofilm do not degrade the protective matrix within the biofilm. In this study, a guanidine and galactose decorated nanophotosensitizer with oxygen self-sufficient capability, p(GF/GEF)-I, is developed to enhance the permeability of biofilms by positively charging the particle surface and easily binding to the bacteria within the membrane through electrostatic interactions. 90% of the biofilm on enamel surface is eliminated after treatment with p(GF/GEF)-I under laser irradiation. Notably, the nanophotosensitizer inhibits the recolonization of dental biofilms by S. mutans, preventing secondary infections. Furthermore, dental caries in a rodent model are reduced with exposure to nanophotosensitizer. p(GF/GEF)-I is a significantly higher efficacy without damaging the surrounding soft tissue. With further development and optimization, p(GF/GEF)-I shows significant potential as a phototherapeutic agent for the treatment of biofilm-induced diseases.