The long duration of 4 months of postoperative adjuvant chemotherapy is currently recommended for locally advanced rectal cancer after preoperative chemoradiation and surgery. Whether a short duration could be applied in these patients is unknown. So, the purpose of this study is to evaluate the effects on prognosis based on different durations of adjuvant chemotherapy for rectal cancer. We performed a retrospective study of 200 rectal cancer patients who were treated with preoperative chemoradiation and were pathologically graded as ypII and ypIII stages between March 2003 and May 2012. All patients were divided into 2 groups according to the median duration of adjuvant chemotherapy of 2 months. Overall survival (OS) and disease-free survival (DFS) were compared between patients with duration shorter and longer than 2 months in the whole group and subgroups of ypII and ypIII. Recurrence patterns were also analyzed in all subgroups. Multivariate analysis was performed to explore clinical factors that were significantly associated with DFS, local recurrence-free survival, and distant metastasis-free survival. In subgroup of ypII stage, the 5-year OS and DFS were similar between patients in long and short durations of adjuvant chemotherapy. For patients of ypIII stage, although no significant difference was found in OS between patients in short and long durations, DFS was showed to be higher in the group of long duration. Further analysis showed that longer duration of adjuvant chemotherapy could lead to improved control of distant metastasis and no impact on local control. Multivariable analysis indicated that long duration of adjuvant chemotherapy is significantly associated with longer distant metastasis-free survival in patients with ypIII stage, but not in those with ypII stage. A long duration of at least 2 months of postoperative adjuvant chemotherapy is necessary for patients with ypIII stage, whereas it may not be absolutely appropriate for those with ypII stage. Therefore, we suggest a tailored selection of durations of adjuvant chemotherapy for locally advanced rectal cancer.