INTRODUCTION: Streptococcus salivarius K12, a comensal benign probiotic, is an alternative for the treatment of the bad breath. OBJECTIVE: To describe on the Streptococcus salivarius K12, mainly referring the reduction of the bad oral odor. METHODS: Secondary research, through the revision of articles in English, January of 2001 until September of 2011. CONCLUSION: The substitution of bacteria implied in halitosis, for the S.salivarius K12, can reduce the severity of this bother.