Aim: Insertion of a transanal drainage tube is effective in the management of obstructing colorectal cancer.We devised a new method of inserting the transanal drainage tube safely and quickly using a thin endoscope.Methods: Sixteen patients (7 men and 9 women) with obstructive left-sided colorectal cancer were treated by inserting a transanal drainage tube using a thin endoscope. We inserted a transanal drainage tube for 32 patients (21 men and 11 women) of left-sided colorectal cancer by conventional method.Results: Drainage tube placement by conventional method was successful in 29 (90.6%) of 32 patients, while, via new method, it was successful in all 16 patients without major complications. Moreover, median insertion time was significantly shortened (34 minutes for the new method compared with 42 minutes for the conventional method).Conclusion: Management of acute colorectal obstruction by transanal drainage tube insertion using the thin endoscope was effective and safe.