To determine serum antibody against human and bacterial heat shock protein (HSP) 60/70 in myeloperoxidase (MPO)-specific anti-neutrophil cytoplasmic autoantibody (ANCA) positive microscopic polyangiitis (MPA), 58 patients with MPO-ANCA positive MPA, 48 with RA (rheumatoid arthritis) and 40 with SLE (systemic lupus erythematosus) were studied. Serum antibodies against HSP (human HSP 70, human HSP 60, Mycobacterium HSP 70, and Escherichia coli HSP 60) were measured by sandwich ELISA. The frequency of anti-human HSP 60/70 antibody positive patients was significantly greater in MPO-ANCA positive MPA than SLE and healthy controls. Anti-human HSP 60/70 antibody titers in patients with MPO-ANCA positive MPA were significantly higher than those of healthy controls; anti-bacterial HSP 60/70 antibody titers were also higher. There was a significant correlation between titers of anti-human HSP 70 antibody and anti-Mycobacterium HSP 70 antibody. A correlation was also found between titers of anti-human HSP 70 antibody and anti-human HSP 60 antibody. Anti-human and bacterial HSP 60/70 antibody titers changed in parallel with disease activity in patients with antibody positive MPA. The anti-HSP antibody titer was also increased in patients with RA and SLE. These results suggest that an immunological background via anti-HSP 60/70 antibodies might be associated with pathogenesis in MPO-ANCA positive MPA.