Aim: For the treatment of polydipsia, medication and occupational therapy are implemented. Since polysipsia canʼt be completely intercepted, patients are isolated or restrained in severe case. Determining the predictive factors of polysipsia may lead to decreasing abnormal water consumption. This study aimed to reveal the influence of subjective oral dryness, salivary volume and other factors including medication on polydipsia in patients with schizophrenia. Methods: Fifty-two patients were divided into two groups: a polydipsia patient (PD) group and a non-polydipsia patient (NPD) group. Their age, medical history, age of onset of schizophrenia, duration of suffering, tobacco, frequency of mouth opening, subjective oral dryness, number of medications, number of xerogenic medications, chlorpromazine (CPZ) equivalent dose, salivary volume and salivary spinability were investigated. Results: The number of total medications was significantly higher than that of the NPD group. Subjective oral dryness of the PD group was rated as ʻsevereʼ compared with the NPD group, and the frequency of mouth opening in the PD group was higher than the NPD group, though there were no significant differences. There was no significant difference in salivary volume and spinability between the two groups. Logisticregression analysis that demonstrated the predictors of polydipsia were tobacco and number of medications. Conclusion: It was shown that the predictors of polydipsia were tobacco and number of medications. The polydipsia may reduce by decreasing medications and quitting tobacco.