Aim To evaluate the clinical effect of delayed thrombolytic therapy with low dose urokinase in acute myocardial infarction. Methods 66 cases of acute myocardial infarction with 12 h to 24 h after onset were divided randomly into two groups, low dose UK group (n=30) and aspirin plus heparin group (n=36). In low dose UK group, low dose UK 5 kIU/kg was given per half hour for 5 consecutive days. Results The number of patients with frequent angina was significant decrease in patients treated with low dose UK as compare with patients in aspirin plus heparin group, the differences were significant (first week: 26.7% vs 36.1%, p<0.05). The rate of heart failure was much lower in low dose UK group than aspirin plus heparin group, the differences were significant (13.3% vs 33.3%, p<0.05). There was no statistically significant difference in four week mortality(3.3% vs 2.8%, p>0.05). Frequency of shock, cardiac arrhythmias, adverse bleeding actions had no statistical significance between the two groups. Conclusion The number of patients with frequent angina and the rate of heart failure might be reduced by using low dose UK in acute myocardial infarction with 12 h to 24 h after onset.