Aim To explore the predictive value of serum microRNA-145 (miR-145) and miR-146a for postoperative coronary slow flow/no reflow (CSF/NRF) in patients with acute coronary syndrome (ACS) undergoing percutaneous coronary intervention (PCI). Methods From January 2020 to January 4,3 patients with ACS who admitted to Caidian District People's Hospital were gathered. They were divided into normal blood flow group (n＝262) and CSF/NRF group (n＝61) based on whether they experienced CSF/NRF after PCI. Relative expression of serum miR-145 and miR-146a was detected by RT-qPCR. General clinical data were collected and analyzed. Logistic regression analysis was applied to analyze the influencing factors of CSF/NRF in patients after PCI. Receiver operating characteristic (ROC) curve was plotted to analyze the predictive value of serum miR-145 and miR-146a for the occurrence of CSF/NRF in patients after PCI. Results Compared with the normal blood flow group, the relative expression level of serum miR-145 was greatly reduced in the CSF/NRF group, while patients in the CSF/NRF group had significantly higher levels of C-reactive protein (CRP) and brain natriuretic peptide (BNP), and the relative expression level of miR-146a (P＜0.05). Increased levels of CRP, BNP and relative expression of miR-146a were risk factors for CSF/NRF in patients (P＜0.05), while increased relative expression of miR-145 was a protective factor for CSF/NRF in patients (P＜0.05). The area under the curve (AUC) of serum levels of miR-145, miR-146a, and their combination for predicting postoperative CSF/NRF in patients was 0.3,0.811, and 0.920, respectively. The combined prediction was greatly better than miR-145 (Z＝2.919, P＝0.004) and miR-146a (Z＝3.341, P＝0.001) alone prediction. Conclusion Serum miR-145, miR-146a in patients with ACS has an adjunctive predictive value for CSF/NRF occurrence after PCI.