Diamond-like carbon (DLC) coatings were deposited on nearly equiatomic nickel-titanium (NiTi) alloy by arc-enhanced magnetron sputtering. The microstructure, surface morphology, chemical composition, surface free energy, protein adsorbance, and leach amount of Ni ions were assessed by Raman spectroscopy, high-resolution transmission electron microscopy (HR-TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), contact angle measurements, micro BCA™ protein assay kit, and inductively coupled plasma mass spectrometry (ICP-MS). The biological response of the endothelial cells (ECs) was evaluated by cell adhesion, morphology, viability, and expression levels of thrombogenicity-related genes. Our results show that the DLC coatings inhibit the release of Ni ions from the NiTi substrate effectively thus enhancing its biosafety. The easy adhesion, elongated morphology, and high viability of ECs on the DLC coatings suggest fast endothelialization after implantation and so application of DLC coatings improves the surface properties of NiTi in cardiovascular applications. The relationship between the surface characteristics, Ni leaching, and concomitant biological response are discussed in details. © 2011 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2012.