BackgroundRecent studies have demonstrated a correlation between intestinal flora and the severity of myocardial infarction as well as post-myocardial infarction repair. However, few studies have investigated whether probiotics reduce mortality and improve cardiovascular outcomes in patients with acute myocardial infarction. In this study, we will conduct a randomized controlled trial (RCT) to evaluate the effect of probiotics on in-hospital mortality and the incidence of major adverse cardiovascular events (MACE) in patients with acute myocardial infarction (AMI).MethodsThis is an open-label, randomized, controlled, superiority clinical trial involving 2594 adult patients who were diagnosed with acute myocardial infarction. Patients will be randomized to (1) receive bifidobacteria triple viable capsule (Bifidobacterium longum,Lactobacillus acidophilus, andEnterococcus faecalis) 840 mg, twice a day, plus standard treatment strategy during the hospital stay, for a maximum of 30 days, or (2) receive the standard treatment strategy and will not take the bifidobacterium triple live capsule. The primary outcome was in-hospital all-cause mortality.DiscussionThe purpose of this clinical trial is to determine whether probiotics can reduce in-hospital mortality and improve prognosis in patients with AMI, and the results will provide evidence for probiotics as a complementary treatment for AMI.Trial registrationChinese Clinical Trials Registry ChiCTR2000038797. Registered on 2 October 2020.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13063-023-07443-5.