Aim To study the effect of different dosages of ticagrelor on the efficacy and renal function in elderly (＞70 years) patients with acute coronary syndrome (ACS) combined with moderate chronic renal insufficiency (CRI). Methods 72 patients with ACS and CRI were randomly divided into full-dose group (36 cases) and half-dose group (36 cases). On the basis of routine treatment of the coronary heart disease and renal insufficiency, patients in full-dose group were treated with full-dose ticagrelor (loading dose 180 mg, followed by 90 mg/times, 2 times/day); patients in half-dose group were treated with half-dose ticagrelor (loading dose 90 mg, followed by 45 mg/times, 2 times/day). The platelet inhibition rate (PIR), serum creatinine (Scr) and alanine aminotransferase (ALT) were detected and the estimated glomerular filtration rate (eGFR) was calculated in the two groups before treatment, after treatment 1,3, 6,2 months, the ischemic events, bleeding events and drug adverse reaction were followed up after treatment within 12 months. ResultsAfter treatment for 1 months, 3 months, 6 months and 12 months, the PIR and Scr in the two groups had an increased trend and the eGFR had a decreased trend compared with before treatment. There was no significant difference in PIR between the two groups (F＝3.679, P＝0.059), Scr and ALT in the half-dose group was significantly lower than those in the full-dose group (F＝234.8,9.451, P＝0.0,0.000), eGFR in the half-dose group was significantly higher than that in the full-dose group (F＝54.521, P＝0.000). After 12 months of follow-up, there was no significant difference in the incidence of ischemic events between the two groups (χ²＝0.050, P＝0.824), incidence of bleeding events and incidence of dyspnea in the half-dose group were lower than those in the full-dose group (χ²＝5.8,5.030, P＝0.3,0.025). Conclusion For elderly patients with ACS and moderate renal insufficiency, there is no significant difference in PIR value between half-dose and full-dose of ticagrelor, but the effect of half-dose of ticagrelor on renal function and liver function is less, bleeding rate is low, and safety is better.