Background: Heavy metal ions can cause allergic and inflammatory reactions that might be associated with in-stent restenosis. This randomized multicenter clinical study was designed to determine if carbon ion-implanted stents reduce luminal late loss by blocking heavy metal ion diffusion into the surrounding tissue. Methods: A total of 225 patients with 230 native coronary lesions were randomly assigned to receive either a carbon ion-implanted Arthos Inert stent (group 1, n = 113) or a bare metal Arthos stent (group 2, n = 117). The primary endpoint was in-stent luminal late loss at 6-month angiographic follow-up, and the secondary endpoints were the 6-month angiographic restenosis rate and the occurrence of the major adverse cardiac events (MACE) including death, nonfatal myocardial infarction, and target lesion revascularization at 12 months. Results: The baseline characteristics were similar in the 2 groups. In-hospital events did not occur in any patients. Angiographic follow-up at 6 months was obtained in 184 lesions (80%). At follow-up, the luminal late loss was similar in the 2 groups (0.91 ± 0.77 mm in group 1 vs 0.88 ± 0.80 mm in group 2, P =. 79), and the angiographic restenosis rates were 11.0% in group 1 and 16.1% in group 2 (P =. 31). The occurrence rates of MACE at 12 months were 9.1% in group 1 and 10.4% in group 2 (P =. 73). Conclusions: The initial and long-term outcomes of the carbon ion-implanted stent were excellent. However, it did not improve long-term outcomes vs the bare metal stent.