The anti-cancer and anti-oxidant activities of methanolic extracts from two indigenous freshwater microalgae (Chlorella vulgaris and Parachlorella sp.) were evaluated in vitro. The extracts from Chlorella vulgaris and Parachlorella sp. contained total polyphenols (236.9 ± 13.3, 223.0 ± 4.5 mg/ g extract, respectively) and flavonoids (14.6 ± 1.3, 31.3 ± 3.1 mg/g extract respectively). Their anti-oxidant activities were evaluated 20 ± 1% and 95 ± 2%, respectively, when treated with 50 mg/mL of the extracts. From the results of cytotoxicity test, both extracts did not inhibited significantly growth of human breast epithelial cells treated with 10 µg/mL to 500 µg/ mL. The microalgal extracts effectively suppressed growth of various cancer cells (DLD-1, MDA-MB 231, MIA PaCa-2 and HCC827). Especially, the extracts from C. vulgaris and Parachlorella sp. effectively inhibited growth of DLD-1 cancer cells (97% and 69%, respectively) when treated with 500 and 1,000 µg/mL, respectively. These results clearly demonstrate that the methanolic extract of C. vulgaris and Parachlorella sp. could be used as a potential natural material as pharmaceutical ingredients.