Abstract: Objective To investigate the regulatory function on physiology and virulence of VicK kinase activity in Streptococcus mutans. Methods PCR ligation mutagenesis was used to construct a vicK knock-out mutant, and kinase activity abolished VicK was expressed by a streptococcal vector in this vicK null mutant. Colony morphology, overnight culture, biofilm formation and gene expression involved in biofilm formation were analyzed. ΔVicK, strains harboring a complemented wild-type vicK, and a vector without insert were used as controls. Results Colonies of VicKH217A were smoother and more elevated than that of wild-type UA159 and complementary strain SMCVicK; cells from VicKH217A overnight culture coaggregated on the bottom of glass tubes; no obvious alteration was observed in VicKH217A biofilm; expressions of gbpB, ftf, gtfD were repressed while gtfB/C were up-regulated (PStreptococcus mutans.