Objective: To investigate whether the dried root of Phellodendron amurense Ruprecht(Phellodendri cortex; PC) extract improves arthritic symptoms through anti-inflammatory and immune-modulatory effects in collagen-induced arthritis in mice. Methods: Rheumatoid arthritis(RA) was induced in male DBA/1 mice by immunization with type Ⅱ collagen(ColⅡ). CIA mice were divided into 5 groups(n=10 per a group) with normal, CIA control, PC extract(50 mg/kg and 100 mg/kg)-treated, and meloxicam(50 mg/kg)-treated as the reference drug. The PC extract or meloxicam were administered orally in CIA mice once a day for 14 days after arthritis induction. Arthritic score, levels of anti-ColⅡ IgG_(2a) antibody, prostaglandin E_2(PGE_2), tumor necrosis factor(TNF)-α, and interleukin(IL)-17 in the sera of CIA mice were measured. Histopathological changes in the ankle joints of CIA mice were also analyzed by staining with hematoxylin and eosin(H and E), safranin-O and immunohistochemistry using anti-TNF-α and anti-IL-17 antibodies. Results: The arthritic score was increased in CIA mice in a time-dependent manner, as were the serum levels of anti-ColⅡ IgG_(2a) antibody, PGE_2, TNF-α, and IL-17. However, the oral administration of PC extract at 50 and 100 mg/kg in CIA mice significantly decreased the arthritic scores, and the serum levels of anti-ColⅡ IgG_(2a), PGE_2, TNF-α, and IL-17 compared with those in the CIA group(P<0.05 or P<0.01). Furthermore, histopathological improvement of the joint architecture in CIA mice was observed after administration of PC extract. PC extract also significantly inhibited the expression of TNF-α and IL-17 in the joints of CIA mice by suppressing the expression of their m RNA and proteins. Conclusion: PC extract may improve the pathological progression of RA through the inhibition of joint destruction by synovial inflammation and immune-stimulation, therefore, it would be a potential anti-arthritic agent in RA. Objective: To investigate whether the dried root of Phellodendron amurense Ruprecht (Phellodendri cortex; PC) extract improves arthritic symptoms through anti-inflammatory and immune-modulatory effects in collagen-induced arthritis in mice. Methods: Rheumatoid arthritis (RA) was induced in male CIA mice were divided into 5 groups (n = 10 per a group) with normal, CIA control, PC extract (50 mg / kg and 100 mg / kg) -treated , and meloxicam (50 mg / kg) -treated as the reference drug. The PC extract or meloxicam were administered orally in CIA mice for a day for 14 days after arthritis induction. Arthritic score, levels of anti-Col II IgG2a antibody , Histopathological changes in the ankle joints of CIA mice were also analyzed by staining with hematoxylin and eosin (PGE 2), tumor necrosis factor (TNF) -α, and interleukin (IL) -17 in the sera of CIA mice were measured. (H and E), safranin-O and immunohistochemistry using anti-TNF α and anti-IL-17 antibodies. Results: The arthritic score was increased in CIA mice in a time-dependent manner, as were the serum levels of anti-Col II IgG_ (2a) antibody, PGE_2, TNF- -17. However, the oral administration of PC extract at 50 and 100 mg / kg in CIA mice significantly decreased the arthritic scores, and the serum levels of anti-Col II IgG_ (2a), PGE_2, TNF-α, and IL-17 Furthermore, histopathological improvement of the joint architecture in CIA mice was observed after administration of PC extract. PC extract also significantly inhibited the expression of TNF-α and IL- 17 in the joints of CIA mice by suppressing the expression of their m RNA and proteins. Conclusion: PC extract may improve the pathological progression of RA through the inhibition of joint destruction by synovial inflammation and immune-stimulation, therefore, it would be a potential anti-arthritic agent in RA.