Background: Systemic corticosteroid use is undeniable for many patients, and many require long-term use of such drugs. Corticosteroids have adverse and irreversible effects on all organs of the body. One of these complications that have not been studied fully is the drug effect on salivary gland function and the quantity and quality of saliva. Some of the many properties of saliva affected by these drugs are saliva pH and viscosity changes and, therefore, its effect on oral health. Methods: This study was performed on 90 cumulative saliva samples containing three groups of corticosteroid users, including more than 15 mg/day, corticosteroid users less than 15 mg/day, and healthy and non-drug users. Each group contained 30 samples. The unstimulated cumulative saliva of volunteers was collected by spitting method for 5 minutes, and the pH of the samples were measured by digital pH meter, and the viscosity of the samples was calculated based on the comparison of the amount of movement of saliva in the capillary tube in millimeter per second with the control fluids. Statistical analysis was performed by Statistical Package for Social Sciences (SPSS V. 18) software and the analysis of variances (ANOVA), Tukey’s multiple comparisons, or their nonparametric equivalents tests were used. Results: The viscosity of saliva in patients with corticosteroid > 15 mg/day was higher than the healthy subjects (P = 0.028). Also, salivary pH in patients taking corticosteroid < 15mg/day was lower than healthy ones (P = 0.017). There was no significant relationship between gender with pH and salivary viscosity (P = 0.933). Conclusions: Long-term consumption of corticosteroids reduces the pH of saliva and increases its viscosity. Therefore Corticosteroids can cause quantitative and qualitative changes in saliva. It also can affect oral and dental health. Hence, the oral health of people taking corticosteroids should be more noticed.