In order to investigate the effects of the extracts from different parts of aquatic vegetables on the proliferation of human hepatoma HepG2 cells and human gastric cancer SGC7901 cells. In this study, 15 kinds of alcohol extracts and 15 kinds of water extracts were obtained from different parts of 7 common aquatic vegetables including water chestnut, gordon euryale seed, lotus root, water taro, wild rice stem, chufa and arrowhead. The effects of different extracts on the proliferation of human liver cancer HepG2 and human gastric cancer SGC7901 cells were detected by the CCK-8 method. The results showed that the alcoholic extract of water chestnut shell, alcoholic extract of euryale shell and water extract of euryale shell exhibited significant and dose-dependent inhibitory effects on the proliferation of HepG2, with the inhibition rates being 70.2%, 83.52% and 71.89% respectively, at 400 μg/mL (the inhibition rate of positive drug, the entafluorouracil (5-Fu), was 73.19% at the same concentration). The alcoholic extract and water extract of water chestnut shell, alcoholic and water extracts of euryale shell, alcoholic extract of euryale flesh, alcoholic extract of lotus root, and alcoholic extract of water chestnut peel exhibited significant inhibitory effect on SGC7901 proliferation in a dose-dependent manner, with the inhibition rates at 400 μg/mL as 58.86%, 46.79%, 41.27%, 67.11%, 49.93%, 57.3%, and 58.96% respectively (the inhibition rate of 5-Fu was 49.33%). Pearson correlation analysis revealed that the effects of aquatic vegetable extracts on tumor cell proliferation were related to the contents of flavonoids and polyphenols.