Background: Exposure to nanoparticles (NPs) can occur in a variety of occupational situations. Ultrafine particles of natural and anthropological origin toxicity has been described in epidemiological studies. Meanwhile, the risks associated with NPs exposure are not comprehensively assessed. A wide spectrum of NPs toxicity has been demonstrated, mainly through the induction of oxidative stress and inflammatory mediators. Among the newly described mechanisms of NPs toxicity is the induction of fibrosis via the epithelial-mesenchymal transition (EMT), which is also a key mechanism of cancer metastasis. The effect of NPs on EMT in the context of metastasis has not been sufficiently described so far, and the results of studies do not allow for the formulation of unambiguous conclusions. Therefore, the aim of the work was to determine the biological activity of silver NPs against MDA-MB-436 triple-negative breast cancer cells. Material and Methods: Reverse transcription real-time polymerase chain reaction was used to examine mRNA expression of EMT markers. The QCM Chemotaxis Cell Migration Assay and QCM ECMatrix Cell Invasion Assay were used to assess the level of cell migration and invasion. The tumor growth factor beta 1 (TGF-beta 1) secretion was determined by the immunoenzymatic method using the Human TGF-beta 1 ELISA Kit. Results: Silver nanoparticles (AgNPs) cause a statistically significant increase in relative expression of all tested mesenchymal EMT markers – cadherin 2, vimentin, matrix metalloproteinase 2 and matrix metalloproteinase 9. At the same time, reduction of epithelial cadherin 1 expression was observed. The level of MDA-MB-436 migration and TGF-beta 1 secretion was slighty increased in AgNPs-treated cells, with no influence on invasion potential. Conclusions: Potentially prometastatic effect of AgNPs encourages further work on the safety of nanomaterials. Med Pr Work Health Saf. 2023;74(6):541–8.