Background: Balneotherapy (BT) is a treatment modality that uses the physical and chemical effects of water, including thermomineral, acratothermal, and acratopegal waters. It has many effects on cardiovascular system. Aim: The aim of the study is to investigate the effects of 3-week BT on blood pressure of osteoarthritis (OA) patients with no hypertension (HT), and controlled or uncontrolled HT. Materials and Methods: The OA patients (n = 270) were divided into three groups: No HT, controlled HT, and uncontrolled HT. All the groups received BT in the facilities of our university hospital at the same time every day (10: 00-11: 30 AM) for 10 min per day, 5 days per week, for a total duration of 15 days in a 3-week period. Systolic and diastolic blood pressures and pulse rates were measured before and after BT on daily basis. Results: Overall, (1) the pulse rates of study groups measured after BT were significantly increased compared to before BT; (2) the systolic blood pressures of study groups measured before and after BT were found as comparable; and (3) the diastolic blood pressures of no HT and controlled HT groups measured before and after BT were not statistically significant (P > 0.05); however, in the uncontrolled HT group, the diastolic blood pressure showed a decreasing trend after BT (P < 0.05). Conclusions: In patients with OA, BT can be safely used without resulting in any meaningful changes in systolic and diastolic blood pressures in patients with normal and controlled HT but a decrease in diastolic blood pressure of patients with uncontrolled HT. This may be an advantage in OA patients having HT as comorbid disease.