This study investigated the antioxidant effects of Spirulina extract on human lung cancer cells (A549) and normal human foreskin fibroblast cells (HFF). The results demonstrated that treatment with Spirulina extract led to a significant decrease in cell viability in A549 cells compared to HFF cells, increased reactive oxygen species (ROS) and malondialdehyde (MDA) production, and induced cell cycle arrest in the G₂ phase, suggesting its potential as a natural anticancer agent against lung cancer cells.