Background: Colonoscopic insertion of a self-expandable metallic stent (SEMS) has been widely performed for the treatment of malignant colorectal obstruction. Different types of stents could influence the efficacy and complication rate of stent use. Objective: To compare the efficacy and complication rates between two SEMSs, the uncovered WallFlex stent and the covered Comvi stent. Design: A prospective, randomized study. Setting: Tertiary-care academic medical center. Patients: Between 2007 and 2009, a total of 151 patients with malignant colorectal obstruction were enrolled. Intervention: Two types of colorectal SEMSs (the uncovered WallFlex stent by Boston Scientific Corp and the newly developed covered Comvi stent by Taewoong Medical Co) were inserted. Main Outcome Measurements: Technical success, clinical success, stent patency, and complication rate according to stent type. Results: Technical failure occurred in 2 patients (1.3%); one was in the WallFlex group and the other in the Comvi group. Clinical failure developed in 9 patients (6.0%): 6 patients from the WallFlex group and 3 from the Comvi group. Complications because of cancer infiltration occurred more frequently in the WallFlex group (14.5% vs 3.8%). However, the rate of stent migration was higher in the Comvi group (21.1% vs 1.8%). The mean patency of the stent did not differ between the two groups (P = .50). Limitations: This was a single-center study. Conclusion: Both uncovered WallFlex and covered Comvi stents were suitable for relieving malignant colorectal obstruction. Tumor ingrowth was more common in the WallFlex group, but stent migration was more common in the Comvi group.