The present study is a double-blind, placebo-controlled, randomized trial to investigate the effect of probiotic supplementation on lipid profile in women with rheumatoid arthritis. Sixty patients attending the rheumatology clinic of Sina hospital or Sheykholrayis clinic will be recruited and randomly assigned to receive either the intervention or the placebo. Inclusion criteria for the patients will be: patients diagnosed with rheumatoid arthritis, based on ACR criteria; having inactive to moderate rheumatoid arthritis; under treatment with DMARDs (Methotrexate, Hydroxychloroquine and Prednisolone less than 10 milligrams per day) and not receiving NSAIDs or cytokine inhibitors; stable medication for at least 3 month prior to the interventions; having body mass index (BMI) less than 40; willing to participate in the study; ages between 20 and 80. Exclusion criteria will include: pregnant and lactating women; hormone therapy or receiving oral contraceptives; having diabetes mellitus, thyroid disorders, kidney or hepatic diseases or Cushing's syndrome; having inflammatory bowel disease or other inflammatory disorders; having digestive tract disorders or lactose intolerance; taking antioxidant, vitamin, fiber or omega-3 supplements 3 weeks prior to the interventions; using antibiotics a month prior to the interventions; being on a weight reduction diet; smoking or being exposed to cigarette smoke; using other probiotic products. The intervention group will receive one 250 milligram capsule containing 10 (8) colony forming unit (CFU) Lactobacillus. casei each day, for 8 weeks; the other group will take one placebo capsule a day for the same period of time. At baseline and at the endpoint of the study, weight and height will be measured and BMI will be calculated; physical activity and psychological stress of the patients will be assessed using the relevant questionnaires; dietary intake of the participants will be evaluated by one 24 hour dietary recall questionnaire and 3 dietary record questionnaires. The serum level of triglyceride, total cholesterol and HDL cholesterol will be measured using commercial kits and spectrophotometry technique at baseline and endpoint of the study. Serum LDL cholesterol will be calculated using Friedewald equation. Arylesterase activity of the paraoxonase enzyme will be measured in the serum samples, using phenyl acetate and by spectrophotometry.