We evaluated the significance of platelet activation in patients with rheumatoid arthritis (RA). The expression of CD62P and CD63 by platelets was determined using flow cytometry in 18 active RA patients, 10 remission RA and 15 normal controls. Meanwhile, the erythrocyte sedimentation rate (ESR) and C-reactive protein was also determined in all groups. The expression of CD62P in active RA patients (11.88 +/- 2.47%) was significantly higher than that in remission RA group (2.85 +/- 1.60%; P < 0.01) and control group (2.78 +/- 1.04%; P < 0.01). The expression of CD63 in active RA patients (9.90 +/- 3.02%) was significantly higher than that in remission RA group (4.11 +/- 2.00%; P < 0.01) and control group (4.13 +/- 1.85%; P < 0.01). The level of CRP (54.33 +/- 23.35 mg/l) and ESR (86.06 +/- 33.67 mm/h) in active RA patients was higher than that in remission RA group (2.55 +/- 1.01 mg/l, 14.70 +/- 4.57 mm/h; P < 0.01 for both) and normal control group (3.21 +/- 2.18 mg/l, 12.25 +/- 5.05 mm/h; P < 0.01 for both). There was a positive correlation between CD62P and ESR (r = 0.5224, P < 0.01) and also a positive correlation between CD62P and CRP (r = 0.7048, P < 0.01) as well as between CD63 and ESR (r = 0.4476, P < 0.05) but no correlation between CD63 and CRP. Platelet activation may be a sign of RA exacerbation.