Cetuximab is an IgG1 chimeric mAb against epidermal growth factor receptor, which can be used for chemotherapy failure or tolerance in patients with epidermal growth factor receptor expressed RAS wild-type metastatic colorectal cancer. We report on a patient who developed rapid-onset interstitial pneumonia while being treated with cetuximab plus XELOX (oxaliplatin, capecitabine) for metastatic colorectal cancer. A 75-year-old man patient was administered cetuximab plus XELOX regularly. After his cetuximab schedule was adjusted from 1 to 2 weeks, he rapidly developed interstitial pneumonia which led to acute respiratory distress syndrome. Our literature review indicated that, for patients with risk factors, a 2-week regimen of cetuximab might lead to interstitial pneumonia. Clinicians should closely monitor patients for adverse drug reactions to improve drug safety.