Adipocytokines, including adiponectin, resistin, and visfatin may play an important role in the pathophysiology of osteoarthritis (OA). Spa therapy is one of the most commonly used non-pharmacological approaches for OA, but its mechanisms of action are not completely known. The aim of the present study was to assess whether a cycle of mud-bath therapy (MBT) influences the serum levels of adiponectin, resistin, and visfatin in patients with knee OA. As part of a prospective randomized, single blind-controlled trial evaluating the efficacy of MBT in knee OA, we included in this study 95 outpatients. One group (n = 49) received a cycle of MBT at the spa center of Chianciano Terme (Italy) in addition to the usual treatment, and one group (control group; n = 46) continued their regular care routine alone. Patients were assessed at basal time and at the end of the study (15 days) for clinical and biochemical parameters. Clinical assessments included spontaneous pain on a visual analog scale (VAS) score and the Western Ontario and McMaster Universities index (WOMAC) subscores for knee OA evaluated as total pain score (W-TPS), total stiffness score (W-TSS), and total physical function score (W-TPFS). Adiponectin, resistin and visfatin serum levels were assessed by enzyme immunoassay methods. At the end of the mud-bath therapy, serum adiponectin levels showed a significant decrease (p < 0.001), while no significant modifications were found in the control group at day 15. Serum resistin showed a significant decrease (p < 0.0001) in the MBT group at the end of the study and a significant increase in the control patients (p < 0.001). No significant modifications of visfatin were found in MBT. Furthermore, we tested the relationships between demographic and clinical parameters and adipocytokine concentrations measured in the MBT group at basal and at the end of the study. In conclusion, the present study shows that a cycle of MBT can modify serum levels of adiponectin and resistin but not the circulating levels of visfatin. In view of the recent evidences about the involvement of adiponectin and resistin in the pathogenesis and progression of OA, the decrease of these adipokines after mud-bath therapy may play a protective role in the course of the disease. However, it remains to be clarified which of the mechanisms of action of MBT may have determined the changes in serum levels of adiponectin and resistin that we observed.