Objectives The purpose of this study was to know the effects of Danggwisayeok-tang (Dangguisinitang) extract (DGSYT) on monosodium iodoacetate (MIA)-induced rat osteoarthritis. Methods For this purpose, rats were divided into 5 groups. Normal group was not injected with MIA and orally administered any medication. Control group was injected with MIA and not orally administered any medication. DGSYT100 group was injected with MIA and orally administered 100 mg/kg of DGSYT. DGSYT300 group was injected with MIA and orally administered 300 mg/kg of DGSYT. JoinsT group was injected with MIA and orally administered 20 mg/kg of Joins tablet. DGSYT100 and DGSYT300 groups were orally administered DGSYT during a week before and 3 weeks after based on the day MIA injected. The changes of hepatotoxicity, nephrotoxicity, relative hind paw weight distribution, cytokine in serum, cytokine messenger ribonucleic acid (mRNA) in joint tissue and histopathological observation (Hematoxylin & Eosin and Safranin-O staining) were measured. Results Alanine aminotransferase (ALT) levels of DGSYT100, DGSYT300 and JoinsT groups were increased significantly, but these results were within normal range. Aspartate aminotransferase (AST) and creatinine levels of all groups were not changed significantly. In the change of relative hind paw weight distribution, DGSYT300 and JoinsT groups were decreased significantly 14 and 21 days after MIA injected. Interleukin-1β (IL-1β) and Interleukin-6 (IL-6), Leukotriene B4 and Osteocalcin levels of DGSYT300 and JoinsT groups were decreased significantly. In measurement of IL-1β and nitric oxide synthase-Ⅱ mRNA relative quantitative of control, DGSYT100, DGSYT300 and JoinsT groups were decreased significantly. In measurement of TNF-α, IL-6 and Cyclooxygenase-2 mRNA relative quantitative of control, DGSYT300 and JoinsT groups was decreased significantly. In histopathological observation of knee, synovial tissue, cartilage and proteoglycan of DGSYT100, DGSYT300 and JoinsT were well preserved compared with control group. Conclusions According to the results, DGSYT has anti-inflammation and pain relief effects. So it should be suppressed progression of arthritis in MIA-induced osteoarthritis rat. (J Korean Med Rehab 2015;25(2):37-50)