Anastomotic leakage (AL) after left-sided colorectal cancer surgery is one of the most serious complication. Once anastomotic leakage occur, we have to select the treatment, non-surgical or surgical. The aim of this study is to evaluate the outcome of the treatments for AL after left-sided colorectal surgery in our institution. Fifty-five patients who had AL after left-sided colorectal surgery were included in this study. Thirty nine were treated for non-surgical treatment (non-surgical group). In eight patients, we had to change the strategy from non-surgical to surgical during non-surgical treatment (convert group). Eight patients were treated for surgical treatment at first due to generalized peritonitis (surgical group). There were not significant differences in patient's background and blood examination between these groups. The patients who had three symptoms (the change of drain contents, fever higher than 38℃ and abdominal pain) in convert group were significantly more frequent than those of non-surgical group (50%:7.7% P = 0.01). The rate of diverting stoma in non-surgical group were significantly more frequent than those of convert and surgical groups (25.6%:6.2% P < 0.001). In all of 55 patients, the rate of permanent stoma was 9% and mortality was 0%. In selected patients without generalized peritonitis, AL after left-sided colorectal cancer can be controlled by non-surgical treatment. Furthermore it may decrease the rate of permanent stoma. Moreover, we should select surgical treatment at first step for the patients who had three clinical symptoms even in the absence of findings of generalized peritonitis.