•Results of in silico studies supported those of in vitro studies.•Cyanidin-3-glucoside had the highest inhibitory activity.•The four anthocyanins showed competitive inhibitions against α-amylase.•Side chain of GLU233 was showed to play a key role in the inhibition. The inhibition activities and mechanisms of four anthocyanins including cyanidin-3-glucoside, cyanidin-3,5-glucoside, cyanidin-3-rutinoside, and peonidin-3-glucoside, against porcine pancreatic α-amylase were investigated through in vitro and in silico studies. The in vitro inhibition study demonstrated that the four anthocyanins competitively inhibited porcine pancreatic α-amylase, which was later verified by the in silico molecular docking study that showed all the anthocyanins bound exclusively to the active site of porcine pancreatic α-amylase. Cyanidin-3-glucoside was found to have the highest inhibition activity with the Ki value of 0.014 mM, followed by cyanidin-3-rutinoside, cyanidin-3,5-glucoside, and peonidin-3-glucoside with the Ki value of 0.019, 0.020, and 0.045 mM, respectively. Results obtained from the in silico study also showed that the four anthocyanins were surrounded by the side chains of the active site of porcine pancreatic α-amylase, among which the side chain of GLU233 was supposed to play a key role in imparting the inhibition activity of anthocyanins.