Introduction – Spirulina maxima (Sm), a blue-green microalgae, is well known for its rich nutritional composition, antioxidant, and anti-inflammatory properties. In this study, we found that small extracellular vesicles (sEVs) isolated from Sm exhibit antifibrotic activity. Methods – Sm derived sEVs (Sm_sEV) were purified from the Sm culture medium using tangential flow filtration (TFF), followed by size-exclusion chromatography (SEC). Characterization of the sEVs was performed using nanoparticle tracking analysis (NTA), transmission electron microscopy (TEM), immunogold TEM, surface-enhanced IR spectroscopy (SEIRS), and flow cytometry (FC). Internalization of DiI-labeled sEVs by human primary peritoneal mesothelial cells (P-MCs) and peritoneal fibroblasts (p-FBs) was examined using fluorescence microscopy. The effect of sEVs on mesenchymal transition of P-MCs and activation of P-FBs was investigated by immunofluorescent staining, MTT cell-proliferation, and Sirius Red collagen accumulation assays, respectively. The antifibrotic relevance of Sm_sEV was further investigated in a chlorhexidine digluconate (CG)-induced mouse model of peritoneal fibrosis. Results – The isolated Sm_sEV exhibited a spherical morphology, with a size range of 150.0 ± 67.6 nm, and the protein-to-lipid ratio (P/L_spectr) was 2.27 ± 0.07. The sEVs cargo contained Parkinson’s disease protein 7 (PARK7), and heat shock protein 70 (HSP70). DiI-labeled sEVs were successfully internalized by both P-MCs and P-FBs and inhibited TGF-β-induced mesenchymal transition in P-MCs and the collagen production and PDGF-B-induced proliferation in P-FBs. In vivo, intraperitoneal administration of Sm_sEVs reduced CG-induced submesothelial thickening, fibronectin, and collagen type I alpha 1 immunopositivity, and increased cytokeratin 18, immunopositivity in the mesothelial layer. Discussion – These findings highlight the antifibrotic effect of Sm_sEV and support their further investigation in the context of fibrosis.