Aim To evaluate the efficacy and safety of the national low molecular weight heparin (LWMH)-Livaracine in treating acute coronary syndrome compared with standard heparin (SH). Methods In a randomized clinical trial, 84 patients, with at least one attack of ischemic chest pain by unstable angina or non-Q wave myocardial infarction within 72 h before treatment enrolled, were divided into two groups, group SH: intravenous SH 5 000 IU, twice daily to maintain the APTT or ACT at 1.5～2.0 times of control for 7 days and group LMWH: subcutaneous Livaracine 5 000 IU, twice daily for 7 days. All patients took 150 mg asprins daily at the same time. The primary indexes were the improvement of clinical symptoms and ECG, composite events (acute myocardial infarction,cardiac or noncardiac death and urgent revascularization) and adverse reaction. The patients enrolled should stay in hospital for at least 14 days. Results By 7 days, the incidence of angina pectoris was not significant between the two groups, but more patients needed oral nitroglycerin for pain relief in group SH. By 14 days, composite events were singificantly reduced in group LWMH than in group SH. Serious bleeding was very few in patients receiving LWMH. Conclusions Subcutaneous Livaracine is at least as effectural as continuous intravenous SH for the suppression of heart attacks in the early and late phase of acute coronary syndrome. LMWH is more effective in reducing composite cardiovascular events 14 days after drug initiation. Monitoring is not necessary in the routine use of LMWH, which shows more convenience and ease of use.