Display omitted •SE exerts a cytotoxic and anti-proliferative effect on A549 cells.•SE inhibits A549 cell cycle progression in the G1 phase.•SE induces A549 cell apoptosis.•The results support the knowledge of the chemo-preventive properties of SE. Spirulina is a well-described and popular dietary supplement derived from Arthrospira algae. In the present study, the anticancer potential of a water extract of a commercial Spirulina product (SE) against the human non-small-cell lung carcinoma A549 cell line was evaluated. After qualitative analysis, we investigated the effect of SE on cell viability, proliferation, and morphology. Furthermore, the influence of SE on regulation of the cell cycle, induction of apoptosis in lung cancer cells, and expression of cell cycle/apoptosis-related proteins was evaluated. Additionally, we examined the cytotoxic effect of SE on normal human skin fibroblasts (HSF). Our studies revealed that SE significantly reduced cancer cell viability and proliferation, which was accompanied by cell cycle inhibition in the G1 phase, induction of apoptosis, and prominent morphological changes. Moreover, we detected no cytotoxic effect of the tested Spirulina extract on normal skin fibroblasts. Our molecular studies demonstrated that SE reduced the phosphorylation of Akt and Rb proteins, reduced the expression of cyclin D1 and CDK4, and increased the Bax to Bcl-2 ratio in the A549 cells. In conclusion, the results obtained provide evidence of the anti-cancer activity of the commercial Spirulina product against lung cancer cells and strongly support the knowledge of the chemopreventive properties of Spirulina.