Oxidative stress plays a critical role in the pathogenesis of hypertension; however, there are no data on salivary redox homeostasis and salivary gland function in children with hypertension. A total of 53 children with hypertension and age- and sex-matched controls were classified for the study. The antioxidant barrier and oxidative/nitrosative stress were evaluated in non-stimulated (NWS) and stimulated (SWS) whole saliva, plasma, and erythrocytes, with Student's t-test and Mann-Whitney U-test used for statistical analysis. We demonstrated that the activities of superoxide dismutase, catalase, and peroxidase were significantly higher in NWS, SWS, and erythrocytes of children with hypertension, similar to oxidative damage in proteins (advanced glycation end products) and lipids (malondialdehyde) as well as nitrosative stress markers (peroxynitrite and nitrotyrosine). The level of uric acid (UA) was significantly higher in NWS, SWS, and plasma of children with hypertension. UA concentration in SWS correlated positively with systolic and diastolic blood pressure and UA content in plasma. This parameter differentiates children with hypertension from healthy controls (AUC = 0.98) with a high degree of sensitivity (94%) and specificity (94%). Stimulated salivary flow was significantly lower in the hypertension group, similar to total protein content and salivary amylase activity. In summary, childhood hypertension is associated with hyposalivation as well as disturbances in antioxidant defense and enhanced oxidative/nitrosative damage both in the plasma/erythrocytes as well as saliva. Salivary UA may be a potential biomarker of hypertension in children.