Abstract: In this study, the change of intestinal microflora in rat fecal samples after amoxicillin administration was observed. In vitro incubation experiments combined with LC-MS/MS assay were used to test the role of intestinal flora in the metabolism of nifedipine. The effect of changes of intestinal flora was determined after amoxicillin administration on the metabolism of nifedipine. We found that the number and types of intestinal flora decreased after taking amoxicillin. After incubation for 12 h, the results showed that the remaining amounts of nifedipine in the N1 group (nifedipine) and N2 group (amoxicillin + nifedipine) were 0.057 6 and 0.064 8 μmol·L^-1, respectively, while the remaining amounts of nifedipine after 24 h of incubation were 0.039 6 and 0.050 4 μmol·L^-1, respectively. These results show that the intestinal flora is involved in the metabolism of nifedipine. After administration of amoxicillin, the metabolism of nifedipine was slowed down, the AUC_0-t was increased by 39.10%, t_max was advanced by 0.45 h, and the CL was reduced 34.71%. The data suggest that the combination may enhance the therapeutic effect of nifedipine. Therefore, drug-drug interactions mediated by gut microbiota cannot be ignored when combined with antibiotics and nifedipine, one of the important factors affecting drug efficacy.