Introduction: Whether high or low ligation of the inferior mesenteric artery (IMA) is optimal for treating sigmoid colon and rectal cancers is controversial. The present study aimed to compare outcomes of high and low ligation of the IMA and determine the adequate extent of IMA lymph node dissection. Methods: Subjects were 455 consecutive stage I–III colorectal cancer patients who underwent curative surgery between 2011 and 2019. We assessed the association between the level of IMA ligation and overall survival and recurrence-free survival (RFS) by propensity score matching analysis. Clinicopathological features of IMA lymph node metastasis and recurrence patterns were analyzed. Results: After propensity score matching, the low ligation group had a significantly worse prognosis than that of the high ligation group for RFS (p = 0.039). Positive IMA lymph nodes were associated with pathological T3 or T4 stage and N2 stage. IMA lymph node recurrences in the high ligation group occurred at the superior left side of the IMA root. In contrast, all recurrences in the low ligation group occurred at the left colic artery bifurcation. Conclusion: High ligation of IMA is oncologically safe. However, even with high ligation, care must be taken to ensure adequate lymph node dissection.