Antibiotics are considered a type of antimicrobial that particularly has an impact on bacteria or fungi in humans and animals. The widespread use of common antibiotics, combined with the fact that the majority of active antibiotics and their metabolites are water-soluble, results in persistent pollution in aquatic environments, as well as a potential threat to ecosystems. Moreover, there are inadequate ecotoxicological data on many antibiotics, such as azithromycin, which has been quantified at elevated levels in the aquatic system. Raphidocelis subcapitata is a globally distributed green alga that is commonly used as a model species for evaluating chemical toxicity due to the availability of a sequenced genome and its rapid growth, which allows assessing chemical effects across many generations. the aim of this project is to provide an insight on genotoxicity for R. subcapitata and study the effects of azithromycin antibiotic on algae, on both growth rate and molecular levels by determining gene expression levels, specifically, its effect related to chlorophyll pigments,biosynthesis, and DNA replication levels. In order to do that, toxicity test according to OECD guidelines for 7 days, photosynthetic pigment extraction and qRT-PCR were utilized. In the present study, an EC50 of 24 µg/L was obtained, while low risk in the Swedish water streams was indicated, significant induction in Chlorophyll a and b at high concentrations while no effects on carotenoids were observed, no significant difference in pcna and cyt P450 at LOEC and lower concentrations was obtained. This might suggests testing higher concentrations in upcoming research.