<p>This study evaluated the sensitivity of two green microalgae species to clomazone exposure. Clomazone is a widely used herbicide for weed management. Through various runoff and transport mechanisms, clomazone can reach aquatic ecosystems and adversely affect non-target organisms, such as microalgae. We assessed the effects of clomazone on the microalgae <i>Desmodesmus communis</i> and <i>Pseudopediastrum boryanum</i>. Endpoints included photosynthetic pigments (chlorophyll <i>a</i>, chlorophyll <i>b</i>, and carotenoids), oxidative stress indicators (reactive oxygen species [ROS] generation and lipid peroxidation [MDA content]), and enzyme activities (superoxide dismutase [SOD], catalase [CAT], ascorbate peroxidase [APX], glutathione <i>S</i>-transferase [GST], and glycolate oxidase [GO]). Assays were performed across six concentrations (0.0, 0.25, 0.50, 0.75, 1.0, and 1.5 mg L⁻¹) under controlled laboratory conditions. The results revealed species-specific responses: <i>D. communis</i> exhibited significant decreases in chlorophyll-a and carotenoid content, coupled with elevated oxidative stress markers at higher clomazone concentrations (1.5 mg L⁻¹). In contrast, <i>P. boryanum</i> maintained pigment levels and enhanced its antioxidant defense system (SOD and CAT) and GST and GO enzymes, following clomazone exposure. These findings highlight the differential tolerance mechanisms of green microalgae to herbicide-induced stress, with <i>P. boryanum</i> being less sensitive than <i>D. communis,</i> and suggest the potential of <i>P. boryanum</i> for bioremediation application. Overall, this study provides critical insights into the ecological risks of clomazone contamination and underscores the need to further explore microalgal resilience as a strategy for mitigating herbicide impacts on aquatic environments.</p>