Organic solvent and hot water extracts of freshwater macroalgae, Cladophora glomerata and Microspora floccosa, harvested from Nan River in northern Thailand were screened for antioxidant and anticancer activities using DPPH free radical scavenging assay and inhibition of proliferation of the KB human oral cancer cell lines respectively. The ethyl acetate extract of C. glomerata showed the highest total phenol content (18.1±2.3 mg GAE/g), radical scavenging activity (49.8±2.7% DPPH scavenging at

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... 100 g/ml) and in vitro growth inhibition (IC 50 =1420.0±66 g/g) of the KB cell lines. These results indicate that C. glomerata could be a source of valuable bioactive materials.