Pharmacologic agents are considered to be a cornerstone of cancer pain management. Patients' concerns about use of analgesics are likely to lead to poor pain management. The purpose of this study was to describe participants' responses to their beliefs regarding pain and prescribed opioids. Ninety-two outpatients age ≥18 years who had taken prescribed opioid analgesics for cancer-related pain in two teaching hospitals in the Taipei area completed the Pain Opioid Analgesics Beliefs Scale-Cancer. An important finding of this study is that large numbers of patients had misconceptions about using opioids for pain. Between 33.7% and 68.5% of the patients in this study held negative beliefs about opioids and beliefs about pain. Specifically, 68.5% of the patients agreed that "opioid medication is not good for a person's body." Many patients (62%) agreed that "the more opioid medicine a patient used, the greater the possibility that he/she might rely on the medicine forever," and 61.0% agreed that "if a patient starts to use opioid medicine at too early a stage, the medicine will have less of an effect later." Two-thirds (66.3%) of the sample agreed that adult patients should not use opioid medicine frequently. The findings provide empirical support for the need for better programmatic efforts to improve beliefs of pain and analgesics in Taiwanese oncology outpatients.