Purpose: To compare the effects of two different traditional spa therapy regimens for knee osteoarthritis (OA) on function and pain. Patients and Methods: Patients with knee osteoarthritis staying in a spa hotel in Sandikli Spa for traditional spa therapy (8 days) were asked to be included in the study. Total of 49 patients gave informed consent consisting two groups based on treatment regimens as follows: Group I (n = 24) had a thermal water bath and a peloid bath per day; Group II (n = 25) had two thermal mineral water baths per day. The primary outcome measure was Lequesne's knee severity index. Secondary measures were pain intensity (visual analogue scale), 10 meters walking time, 3 times squatting down and up time and 10 stairs stepping up and down time. An unblinded observer carried out all assessments at the beginning and at the end of the spa therapy. Results: In both groups, improvements were found in Lequesne's Knee Index (49.3% in group I and 31.3% in group II, respectively) (p < 0.001) and improvement in group I was significantly higher than group II (p < 0.001). VAS scores for pain reduced in both groups (37.3% and 30.1%) and this reduction was significantly higher in group I (p = 0.003). All other 3 measures also showed significant improvements in both groups and again improvements were significantly higher in group I than group II. Conclusions: Both traditional spa therapy regimens could significantly improve the functional status and pain on patients with knee OA in the present study. Spa therapy combining thermal bath and peloid application seems having better improvement than the therapy with twice-daily thermal baths in knee OA, but this difference may not be clinically relevant.