STA-21 ameliorates CAIA by suppressing RORγt and upregulating of Foxp3. Treatment with STA-21 specifically regulates the JAK1/Stat3 pathway. STA-21 reduces CD8+ and CD14+ cells and increases IL-27+ cells. Action of STA-21 results in regulation of Th1 and Th2 cytokine levels. A Stat3 inhibitor may be a viable therapeutic option for rheumatoid arthritis.