The ability of natural killer (NK) cells to rapidly detect and eliminate tumour cells within the body has led to the pioneering of innovative anti-cancer immunotherapies in recent decades. Adoptive cell transfer of NK cells has now emerged as a promising strategy for cancer treatment, with encouraging results recently seen in phase I/II clinical trials in patients with hematological malignancies. However, NK cell-based therapies have not yet shown similar promise for hard-to-cure solid tumors such as triple negative breast cancer (TNBC). The immunosuppressive tumor microenvironment (TME) of cancers such as TNBC is considered a major barrier to treatment success, with multiple aspects of immunoevasion still in need of being deciphered. In particular, TNBC-derived extracellular vesicles (TNBC-EVs) within the TME and circulating in the body can negatively impact immune functions to facilitate tumor progression, however the precise mechanism/s by which these EVs affect endogenous and therapeutic NK cells remains underexplored. Here, we show EVs isolated by tangential flow filtration from TNBC cell line MDA-MB-231 can attenuate the tumoricidal functions, proliferation, and metabolism of primary human NK cells derived from peripheral blood mononuclear cells. Furthermore, we have identified that glycans on the surface of these TNBC-EVs are responsible for these effects, as NK cell functions can be restored when TNBC-EV glycans are removed. These findings offer new insights into the hurdles that face NK cell therapy success in TNBC and hold significance for future approaches which could be taken to improve the efficacy of NK cellular therapies.