Objective To observe the effectiveness and safety of low-molecular-weight heparin in treatment of elderly patients with acute coronary syndrome (ACS) at high altitude. Methods Ninety elderly patients with ACS who were hospitalized in our department from April 2008 to October 2012 were randomly divided into conventional therapy group (n＝42) and delayed therapy group (n＝48). Patients in conventional group received subcutaneous injection of low-molecular-weight heparin for 5 to 7d, while those in delayed group received same treatment but with duration lasting for 10 to 14d. The basic therapy was similar between the two groups. The incidence of cardiovascular events, hemorrhage and platelet reduction within 30d were recorded. Results The incidence of cardiovascular events within 30d was significantly higher in conventional group than in delayed group (19.0% vs 4.2%, P＜0.05). The incidence of hemorrhage was similar between the two groups (4.8% vs 6.3%, P＞0.05). No reduction in platelet count was observed. Conclusion The strategy of delayed therapy with low-molecular-weight heparin in elderly patients at high altitude with ACS significantly decreases the incidence of cardiovascular events within 30d, but has no effect on hemorrhage risk.