Background and purpose: Marine algae are potential renewable and sustainable sources of bioactive natural products which can be utilized in nutraceutical and pharmaceutical industries. Experimental approach: Different extracts (methanol, chloroform, and ethyl acetate) of red algae, Laurencia snyderiae , was evaluated for their antioxidant potential, with various antioxidant assessment assays, cytotoxic properties (using MTT colorimetric assay), and phytochemical constituents (total phenolic and flavonoid contents). The GC-MS analyses of the algal methanolic extract and its apoptotic effects on the human colon carcinoma cell line (HT29) were also investigated. Findings/Results: The total phenolic content in the methanol, chloroform, and ethyl acetate extracts of L. snyderiae was 3.6 ± 0.12, 3.2 ± 0.41, and 3.3 ± 0.35 μg/mg of gallic acid, respectively. Among different algae extracts, chloroform extract showed significantly chelating ability (IC 50 = 0.027 mg/mL) and reducing power activity (IC 50 = 0.082 mg/mL), while the highest DPPH scavenging activity (IC 50 = 0.058 mg/mL) exhibited in the methanol extract compared to the other extracts. The methanolic extract was found to have a higher cytotoxicity effect on colon carcinoma cells with IC 50 70.2 μg/mL. The viability of the cancer cells was increased with the decrease in the concentration in different extracts. GC-MS analysis of the algal methanolic extract revealed the presence of active antitumor constituents and apoptosis-based cytotoxicity against colon cancer cells through the DNA damage was also confirmed. Conclusion and implications: Based on these results, the red algae L. snyderiae possesses potent bioactive constituents and can use as additional resources as a natural antioxidant and antitumor agent in the pharmaceutical and nutraceutical area.