Abstract: AIM:To observe the effectiveness and safety of delayed therapy with low molecular weight heparin (LMWH) in patients with non-ST segment elevation acute coronary syndrome (NSTE-ACS) at high altitude. METHODS: Eighty-five patients with NSTE-ACS were randomized into conventional therapy group (n=42) and delayed therapy group (n=43). Patients in conventional group received LMWH therapy for 5 to 7 days, whereas patients in delayed group received LMWH for 10-14 days. The basic therapy was similar in both groups. The incidences of cardiovascular events, hemorrhage and platelet reduction within 30 days were recorded. RESULTS: The incidence of cardiovascular events within 30 days in conventional group was significantly higher than that in delayed group (19.0% vs. 4.7%, P<0.05). The incidence of hemorrhage was similar between groups (4.8% vs. 4.7%, P>0.05). No reduction in platelet count and no increase in activated partial thromboplastin time (aPTT) were observed. CONCLUSION: The strategy of delayed therapy with LMWH will significantly decrease the incidence of cardiovascular events in patients with NSTE-ACS at high altitude within 30 days and will not significantly increase hemorrhage risks.