This study investigates the effects of varying concentrations of environmentally friendly synthesized silver nanoparticles on the microalga Dunaliella salina. Silver nanoparticles were synthesized using thyme (Thymus vulgaris L.) extract. The effects of TV-AgNPs on the optical density, cell size, and motility of the microalgae, as well as on biochemical parameters including catalase activity, photosynthetic pigment content, and soluble protein levels, were evaluated. The results demonstrated that even environmentally friendly silver nanoparticles synthesized via the “green” method exerted toxic effects on Dunaliella salina cells, leading to reductions in optical density, cell size, and active motility. Biogenic silver nanoparticles decreased the levels of chlorophyll a and chlorophyll b, while increasing carotenoid content and catalase activity. In addition, exposure to nanoparticles resulted in an increase in soluble protein content. These findings suggest that even biogenic AgNPs induce oxidative stress in Dunaliella salina cells. In response to these adverse conditions, the cells activate protective and adaptive mechanisms to enhance survival.