Chemoselective conjugation of an azido-functionalized thrombomodulin to pancreatic islets was achieved by Staudinger ligation to a surface-bound bifunctional poly(ethylene glycol) linker. The presence of the tethered thrombomodulin resulted in a significant increase in the production of activated protein C with a reduction in islet-mediated thrombogenicity. This report highlights the potential of tissue-targeted chemistry to reduce donor cell mediated procoagulant and proinflammatory responses.