Aim To observe the expression of cyclooxygenase-2 (COX-2) mRNA in peripheral blood monocytes from patients with acute coronary syndrome (ACS), and the effects of atorvastatin on it. Methods Expression of COX-2 mRNA in peripheral blood monocytes from 18 normal control subjects and 42 patients with acute coronary syndrome were analyzed by reverse transcription -polymerase chain reaction (RT-PCR), and the monocytes from patients had been incubated with atorvastatin (0～10 μmol/L)in vitro. Results Expression of COX-2 mRNA significantly increased in peripheral blood monocytes from the patients with ACS compared with those from normal control subjects (1.64±0.25 vs 0.59±0.21, p<0.05). Atorvastatin significantly reduced the expression of COX-2 mRNA in peripheral blood monocytes from patients with ACS (p<0.05), and the reduction is relative to the concentration of atorvastatin. Conclusions These findings suggest that COX-2 may play an important role on the inflammation in atherosclerosis. Atorvastatin may have anti-inflammatory effects which are related to its effect on COX-2.