Microparticles (MPs) are believed to play an important role in inflammatory diseases such as rheumatoid arthritis (RA). Leukocytapheresis (LCAP) is one of the options available for the treatment of RA. We analyzed the levels of MPs in RA, by flow cytometry, especially in relation to the effect of LCAP. Twenty female patients with RA were recruited into this study. Six of the 20 patients with RA further received LCAP. Plasma levels of platelet-derived MPs were high in patients with RA and are correlated with disease activity. LCAP significantly improved RA in all six patients. The numbers of platelet-derived MPs significantly decreased after the first session of LCAP, which was probably due to direct removal by LCAP. Mean numbers of platelet-derived MPs after four sessions of LCAP markedly decreased. The numbers of granulocyte-derived MPs, which are suggested to have an anti-inflammatory effect, were markedly increased after the first session of LCAP. These data suggest that removal of platelet-derived MPs and increase of granulocyte-derived MPs are novel mechanisms of LCAP as effective treatment in RA.