In clinical practice of rheumatoid arthritis (RA), various kinds of laboratory tests are required for diagnosis, assessment of the disease activity, assessment of complications and risk factors before starting therapy, and assessment of adverse effects during the therapy. Anemia, thrombocytosis, and leukocytosis are common in active RA. During RA therapies, liver function tests (including ALT and AST) and renal function tests (including serum creatinine and urinalysis) should be performed. Anti-CCP antibody is an especially useful marker for diagnosis of RA, and the presence of the antibody has been included in ACR/EULAR 2010 RA classification criteria. Reactivation of hepatitis B virus (HBV) after immunosuppressive therapies is a potentially serious complication. HBc and/or HBs antibodies should be measured before starting the therapies even if HBs antigen is negative, and appropriate interventions including measurement of HBV-DNA and starting prophylaxis (entecavir is recommended) should be performed.