Platelet-von Willebrand factor (VWF) is stored within α-granules and accounts for ~20% of total VWF in platelet-rich plasma. This platelet-VWF pool exists distinct from plasma-VWF and is enriched in high molecular weight multimers (HMWM). Previous studies have described significant functional discrepancies between platelet-VWF and plasma-VWF. However the molecular basis responsible for these differences is not well understood. To address this, we have characterized terminal glycan expression on platelet-VWF. Our findings demonstrate that platelet-VWF exists as a distinct natural glycoform. In particular, N-linked sialylation is markedly reduced (>50%) compared to plasma-VWF. Moreover, unlike plasma-VWF, platelet-VWF does not express AB blood group determinants, although precursor H antigen expression is similar to that observed on plasma-VWF. Importantly, as a result of this differential glycosylation, platelet-VWF exhibits specific resistance to ADAMTS13 proteolysis. Thus platelet activation at sites of vascular injury results in the release of high local concentrations of HMWM platelet-VWF that is more resistant to ADAMTS13, thereby facilitating platelet-plug formation.