[ABSTRACT] Objectives To investigate the expression of plasma miR -208b, miR -145 and clinical significance in acute coronary syndrome（ACS）patients. Methods 16 healthy people and 50 ACS patients,including 30 patients with AMI and 20 patients with UAP were enrolled. The plasma samples from ACS patients were obtained within(5±1.4h)（n=50），12h（n=6）and 7d（n=6） after the onset of ACS symtoms. Examing the expression levels of plasma miR -208b and miR -145 by quantitative real-time PCR technology (qRT-PCR) and analyzing the correlation between miR-208b,miR145 expression levels and cTnI,WBC .Results (1) The miR-208b level in plasma from ACS group was higher than that of control group (P <0.05) and the plasma miR208b level in acute myocardial infarction was higher than that of unstable angina group (P <0.05) within (5±1.4h); (2)The miR-145 level in plasma from ACS group was lower than that of in control group(P<0.05) and there is no significant difference of the plasma miR145 expression level in AMI group and UAP group (P >0.05) within (5±1.4h) (3)CTnI which was significantly increased at 6h after ACS remained increased until 12h,and it was restored to the normol value at 7day;both miR208b and miR145 were at their peak values at 6h,and retuned to the control levels at 7d (4)There was positively correlation between of plasma miR208b and cardiac troponin I（cTnI）. (r=0.833, P <0.05)，there was no correlation between plasma miR145 and CTnI（r=0.352，P > 0.05).（5）There was no correlation between of plasma miR208b,145 and WBC（r=-0.243,-0.083，P > 0.05). Conclusion Plasma miR208b is up-regulated and plasma miR145 is down-regulated in ACS. These results suggested that plasma miR208b and miR-145 can be used as a sensitive indicator for ACS.diagnosis.