Percutaneous coronary intervention (PCI) in coronary artery disease (CAD) with very small vessels remains challenging. The aim of this study is to evaluate the safety and effectiveness of the 2.25-mm diameter Ultimaster sirolimus-eluting stent in the treatment of Japanese patients with CAD due to lesions in very small vessels. The CENTURY JSV study is a prospective, multicentre, single-arm study. Seventy patients with lesions deemed suitable for implantation of a 2.25-mm diameter stent were enrolled at seven hospitals in Japan. Patients underwent clinical follow-up at 1-, 9-month, 1-, and 2-year after the PCI procedure. The primary endpoint was the major adverse cardiac event (MACE), a composite of cardiac death, target vessel myocardial infarction (MI), and clinically driven target lesion revascularization (TLR) free rate at 9-month following the procedure. The MACE-free rate was 97.1%, and the lower limit of the two-sided 95% confidence interval (CI) was 90.1%, which exceeded the threshold of 80% set as the performance goal. Angiographic in-stent and in-segment late loss at 9-month were 0.22 ± 0.31 and − 0.02 ± 0.34 mm, respectively. Between 9 months and 2 years, two additional TLRs occurred. Stent thrombosis, bleeding and vascular complication did not occur throughout 2 years. The 2.25-mm diameter Ultimaster ® bioresorbable-polymer sirolimus-eluting stent is safe and effective for treating lesions in very small coronary arteries throughout 2 years after stent implantation. Clinical trial registration: UMIN000012928.