Background: Colonoscopic insertion of self-expandable metallic stent (SEMS) has been widely performed for the treatment of malignant colorectal obstruction. Different type of stents such as covered or uncovered one could influence the patency and complication rate of stents. However, there have been few studies concerning the comparison of efficacy between covered and uncovered stent. Aims and Methods: The aim of this randomized controlled study was to compare the efficacy and patency between two SEMS, i.e., uncovered WallFlex® stent by Boston Scientific and newly developed covered Comvi® stent which surrounded by PTFE (poly tetra fluoro ethylene) by TaeWoong medical Co. Consecutive patients with malignant colorectal obstruction were enrolled between Aug, 2005 and Aug, 2008 at Yonsei University College of Medicine, Seoul, Korea. Results: The total number of 100 patients was included in this study and their pre-procedural clinical characteristics and post-procedural outcomes were evaluated. Demographic characteristics such as sex, age, site, purpose of stent insertion, cause of obstruction were not significantly different between the 2 groups. Among them, fifty seven patients (57%) were treated by WallFlex® stent and forty three patients (43%) by Comvi® stent. Technical failure was developed in 2 patients (2%) who were included in Comvi® group, and clinical failure in 4 patients (4%). In one third of patients (32%), stent insertion was aimed for the bridge to operation, and in two thirds of patients (68%), for the palliation of obstruction. Complications due to cancer infiltration occurred more frequently in the group of WallFlex® stent (20% vs. 7.6%). However, the rate of stent migration was higher in Comvi® group (30% vs. 2.5%). The median patency duration of stent was not different between the 2 groups. Conclusions: Both uncovered WallFlex® and covered Comvi® stents were suitable to relieve malignant colorectal obstruction. Tumor ingrowth was more common in WallFlex® group but stent migration was more frequent in covered Comvi® group.