To clarify the in vitro inhibitory effect and mechanism of the alcoholic extract from Euryale ferox seed shell on human stomach cancer SGC7901 and human liver cancer HepG2 cells. In this study, 75% ethanol was used for ultrasonic extraction of Euryale ferox seed shell and the Folin-Phenol method was used to determine the content of total phenolics; the cell counting Kit-8 (CCK-8) was used to detect the inhibitory rates of the alcoholic extract on the proliferation of SGC7901 and HepG2 cells, and then the IC50 values were calculated. The flow cytometer was used to detect the apoptosis, cell cycle, cell mitochondrial membrane potential and intracellular calcium concentration. The results showed that the alcoholic extract had an inhibitory effect on the proliferation of SGC7901 cells and HepG2 cells, with the inhibition rate being 92.63% and 72.40%, respectively after the treatment with the extract at 200 μg/mL for 48 h. The cell cycle detection showed that the alcoholic extract at 200~800 μg/mL could arrest SGC7901 cells in the G0/G1 phase; the alcoholic extract at 50~200 μg/mL could arrest HepG2 cells in the S phase. The measurements of the cell mitochondrial membrane potential showed that the alcoholic extract could decrease the cell mitochondrial membrane potential of SGC7901 cells and HepG2 cells in a concentration-dependent manner, the cell mitochondrial membrane potential values of SGC7901 cells and HepG2 cells were reduced by 21.92% and 53.81%, respectively, compared with the control group, when the concentration of the alcoholic extract was at 200 μg/mL. The determination of intracellular calcium concentration showed that the alcoholic extract could increase the intracellular calcium ion concentration of SGC7901 cells and HepG2 cells in a concentration-dependent manner. When the extract concentration was 200 μg/mL, the intracellular calcium ion concentrations of SGC7901 cells and HepG2 cells increased by 21.85% and 14.14%, respectively, compared with the control group. Experimental results showed that the alcoholic extract of Euryale ferox seed shell could inhibit the proliferation and induce the apoptosis of SGC7901 and HepG2 cells, and the underlying mechanism might be related to the reduction of cell mitochondrial membrane potential and the increase of intracellular calcium ion concentration.