Xerostomia is the symptom of oral dryness resulting most frequently, but not exclusively, from salivary gland hypofunction. Because the prevalence of xerostomia may increase with age, it has multiple oral health consequences in aging populations. In the present study, we demonstrate that the in vivo administration of 5-aza-2'-deoxycytidine (5-Aza-CdR; decitabine), a DNA demethylating agent, to the murine aging model C57BL/6CrSlc mice (24 wks old) increased the volumes of salivary flow compared with those of control mice. Western blot analysis and immunohistochemical staining demonstrated the augmented expression of AQP5 protein in the salivary glands of 5-Aza-CdR-treated mice compared with those of control mice. In addition, AQP5 protein expression levels in 5-Aza-CdR-treated old mice (27 wks old) were much higher than those in untreated and young mice (6 wks old). Global methylation levels in the salivary glands were significantly lower in the 5-Aza-CdR-treated mice than in the untreated mice. Moreover, the induction of demethylation in the AQP5 promoter of 5-Aza-CdR-treated mice was stronger than in the control mice. Analysis of our data therefore suggests that a DNA demethylating agent may be a useful drug for restoring hyposalivation in elderly individuals, thereby leading to the resolution of xerostomia.