Background: Regorafenib is an oral multikinase inhibitor with a proven survival benefit for metastatic colorectal cancer patients. The KSCC1402/HGCSG1402 study investigated the prophylactic effect of oral dexamethasone (DEX) on regorafenib-related fatigue and/or malaise. Patients and Methods: Patients who progressed after standard chemotherapy were randomized 1: 1 to a DEX group (2 mg/day; days 1–28) with regorafenib or a placebo group with regorafenib. The primary endpoint was the incidence of fatigue and/or malaise, based on version 4.0 of the National Cancer Institute’s CTCAE (Common Terminology Criteria for Adverse Events). One of the secondary endpoints was the in-cidence of fatigue and/or malaise based on the CTCAE assessed by patient-reported outcome (PRO). Results: The incidence of any grade of fatigue and/or malaise assessed by the investigators was 58.8% in the DEX group and 61.1% in the placebo group (p = 0.8101), and that assessed by PRO was 47.2 and 58.3%, respectively (p = 0.3450). The incidence of grade ≥2 fatigue and/or malaise, as assessed by the investigators, was 19.4% for the DEX group and 38.9% for the placebo group (p = 0.0695), and that assessed by PRO was 27.8 and 52.8%, respectively (p = 0.0306). Conclusion: Our results suggest that prophylactic oral DEX is clinically effective in improving regorafenib-related fatigue and/or malaise.