The aim of this study was to evaluate outcomes of inside plastic stents (iPSs) versus those of metal stents (MSs) for treating unresectable perihilar malignant obstructions. For all patients who underwent endoscopic suprapapillary placement of iPS(s) or MS(s) as the first permanent biliary drainage for unresectable malignant perihilar obstructions between January 2014 and August 2019, clinical outcomes using iPSs (n=20) and MSs (n=85), including clinical efficacy, adverse events, and time to recurrence of biliary obstruction (RBO), were retrospectively evaluated. There were no differences in clinical effectiveness (95% for the iPS group vs. 92% for the MS group, p=1.00). Procedure-related adverse events, including pancreatitis, acute cholangitis, acute cholecystitis, and death, were observed for 8% of the MS group, although no patient in the iPS group developed such adverse events. The median time to RBO was 561 days (95% confidence interval, 0-1,186 days) for iPSs and 209 days (127-291 days) for MSs, showing a significant difference (p=0.008). s Time to RBO after iPS placement was significantly longer than that after MS placement. IPSs, which are removable, unlike MSs, were an acceptable option.