Backgorund: Macroalgae are abundant sources of bioactive polysaccharides with various pharmaceutical activity is a prospective candidate for an effective and non-toxic substance. Objective: The purpose of this study is to preliminary characterize and to determine the in vitro antioxidant activity and cancer cell growth inhibitory activity against human lung carcinoma (A549) of the polysaccharide from an invasive green alga, Caulerpa taxifolia. Materials and Methods: Crude polysaccharide (CP) was extracted from the dried algal sample of C. taxifolia by hot water extraction followed by precipitation by absolute ethanol. CP underwent preliminary chemical characterization including protein, carbohydrate, and sulfate content analysis by Kjeldahl titrimetry, acid hydrolysis, gravimetry, and ashing water digestion ion chromatography, respectively. Functional groups present in the CP were determined by Fourier transform infrared spectroscopy (FT-IR). Antioxidant activity was evaluated by 1, 1-diphenyl-2-picrylhydrazyl radical (DPPH) free radical scavenging activity assay. The cancer cell growth inhibitory activity against human lung carcinoma (A549) was evaluated by MTT assay. Results: Chemical composition of the CP shows 68.4 % (w/w) carbohydrate, 9.4% (w/w) protein, and 0.74% (w/w) sulfate. FT-IR shows the presence of -OH group, C-H stretch groups,  C=O groups and C-O groups and suggest a pyranose configuration of the sugar structure. MTT assay shows the highest inhibition at 25 μg/mL concentration with 35.50% ± 1.66 SEM with a relative IC₅₀ of 45.44 μg/mL. However, DPPH assay did not exhibit notable free radical scavenging capacity in contrast with other studies of polysaccharides with only 18.33% at 1mg/mL. Conclusion: This exploratory study on the CP of C. taxifolia may possess a different mechanism of cell death present from other polysaccharide studies and may paved the way in exploring other mechanistic approach on how polysaccharides from marine algae be utilized as a possible anticancer treatment.

Key words: antiproliferative, antioxidant, caulerpa taxifolia, polysaccharide