Dental caries is a common disease caused by oral bacteria. and are the primary cariogenic microbes that often survive as biofilms on teeth. In this study， we evaluated the activity of ClyR， a well-known chimeric lysin with extended streptococcal host range， against common Gram-positive oral microbes and its anticaries efficacy in rat models. ClyR demonstrated high lytic activity against MT8148 and ATCC6715， with minor activity against ， ， and ， which are considered as harmless commensal oral bacteria. Confocal laser scanning microscopy showed that the number of viable cells in 72-h aged and biofilms are significantly ( < 0.05) decreased after treatment with 50 µg/mL ClyR for 5 min. Furthermore， continuous administration of ClyR for 40 days (5 µg/day) significantly ( < 0.05) reduced the severity of caries in rat models infected with a single or a mixed bacteria of and . Therefore， ClyR could be a promising agent or additive for the prevention and treatment of dental caries.