Radiation therapy (RT) is typically applied using one of two standard approaches for preoperative treatment of resectable locally advanced rectal cancer (LARC): short-course RT (SC-RT) alone or long-course RT (LC-RT) with concurrent fluorouracil (5-FU) chemotherapy. The Phase II single-arm KROG 11-02 study using intermediate-course (IC) (33 Gy (Gray)/10 fr (fraction) with concurrent capecitabine) preoperative chemoradiotherapy (CRT) demonstrated a pathologically complete response rate and a sphincter-sparing rate that were close to those of LC-CRT. The current trial aim to compare the pathological/oncological outcomes, toxicity, and quality of life results of LC-CRT and IC-CRT in cases of LARC. The prescribed dose was 33 Gy/10 fr for the IC-CRT group and 50.4 Gy/28 fr for the LC-CRT group. Concurrent chronomodulated capecitabine (Brunch regimen) 1650 mg/m2/daily chemotherapy treatment was applied in both groups. The European Organization for Research and Treatment of Cancer Quality of Life Questionnaire-Colorectal Cancer Module (EORTC QLQ-CR29) was administered at baseline and at three and six months after CRT. A total of 60 patients with LARC randomized to receive IC-CRT (n = 30) or LC-CRT (n = 30) were included in this phase II randomized trial. No significant difference was noted between groups in terms of pathological outcomes, including pathological response rates (ypT0N0-complete response: 23.3% vs. 16.7%, respectively, and ypT0-2N0-downstaging: 50% for each; p = 0.809) and Dworak score-based pathological tumor regression grade (Grade 4-complete response: 23.3 vs. 16.7%, p = 0.839). The 5-year overall survival (73.3 vs. 86.7%, p = 0.173) rate was also similar. The acute radiation dermatitis (p < 0.001) and any hematological toxicity (p = 0.004) rates were significantly higher in the LC-CRT group, while no significant difference was noted between treatment groups in terms of baseline, third month, and sixth month EORTC QLQ-CR29 scores.