Background: The optimal short-course chemotherapeutic regimen for rectal cancer has not been clearly defined until now. KROG 10-01 and KROG 11-02 prospective trials investigated the efficacy and safety of one- and two-week chemoradiotherapy (CRT), respectively. We compare and report long-term outcomes by pooling data from two prospective trials for one- and two-week schedules of preoperative CRT and curative surgery in rectal cancer. Methods: Patients eligible for KROG 10-01 and KROG 11-02 involved those with clinical T3-4N0-2M0 rectal cancers. They received preoperative CRT and total mesorectal excision. Patients in KROG 10-01 received radiation of 25 Gy in 5 fractions during one week with 5-fluorouracil/leucovorin. Patients in KROG 11-02 received radiation of 33 Gy in 10 fractions during two weeks with oral capecitabine. Results: A total of 150 patients consisting of 70 patients from KROG 10-01 and 80 patients from KROG 11-02 were collectively analyzed. With a median follow-up time of 89.2 months, the 5-year overall survival (OS) rate was 86.5% in one-week CRT and 85.3% in two-week CRT (P = 0.84). The 5-year recurrence-free survival (RFS) rate was 83.5% in one-week CRT and 77.1% in two-week CRT (P = 0.45). One patient (1.4%) in one-week CRT and eleven patients (13.8%) in two-week CRT exhibited pathologic complete regression (ypT0N0M0) after radiotherapy (P = 0.01). Downstaging (ypT0-2N0M0) occurred in 20 patients (28.2%) in one-week CRT and 27 patients (33.8%) in two-week CRT (P = 0.50). One-week CRT arm had significantly higher acute hematologic (12.8% vs. 3.8%, P = 0.040) and non-hematologic (38.6% vs. 16.3%, P = 0.002) toxicities than two-week CRT arm. Conclusions: Both one- and two-week schedules of CRT showed favorable survival outcomes after seven years of follow-up. But, two-week course achieved more increased tumor response and decreased acute toxicity rather than one-week course. Clinical trial information: KROG 10-01 is registered at ClinicalTrials.gov (number, NCT01129700) and KROG 11-02 is registered at ClinicalTrials.gov (number, NCT01431599).