Usnic acid (UA) is a secondary metabolite produced by lichens that has attracted interest because of its antimicrobial, photoprotective, and antioxidant properties, suggesting its potential use as a biostimulant in agriculture. However, its evaluation in agricultural crops is limited. In the present study, we evaluated the effect of applying (+) UA on enzymatic and non-enzymatic antioxidant systems, photosynthetic pigments, photosynthetic enzyme activity, and markers of oxidative stress in “Albion” strawberry plants. The plants were grown in a peat moss:perlite substrate (1:1, v/v) and cultivated under tunnel greenhouse conditions using a nutrient solution applied via fertigation. (+) UA was applied at 400 µg/mL via three routes (foliar, drench, and a combination of foliar and drench) on three occasions. Leaf tissue was collected 117 days after transplantation, and the biochemical parameters were quantified. (+) UA increased the activity of glutathione peroxidase (GPX) (53% via foliar-drench) and catalase (CAT) by 73.5% (via drench), and reduced glutathione (GSH) content by 58% (via foliar). β-carbonic anhydrase (βCA) activity increased by 415% and 384% (foliar and foliar-drench, respectively). Likewise, Ribulose 1,5-bisphosphate carboxylase-oxygenase (RuBisCO) activity increased by 58.23% (drench) and phosphoenolpyruvate carboxylase (PEPC) by 25% and 46% (foliar and drench), suggesting positive effects on the processes associated with CO2 assimilation and transport. In contrast, no significant changes were observed in the levels of hydrogen peroxide (H2O2), malondialdehyde (MDA), or proline, indicating the absence of oxidative stress. These findings suggest that (+) UA modulates the enzymatic antioxidant system, promoting favorable physilogical responses without inducing oxidative stress. The use of (+) UA has been proposed as a potential promoter of metabolism in agricultural crops. In addition, new avenues of research are being explored to investigate the role in modulating antioxidant responses under biotic and abiotic stress conditions. Keywords: carbonic anhydrase; RuBisCO; PEP-carboxylase; catalase.