Pain is common in cancer care and patients` self-report of pain is an essential first step in ideal cancer pain management. However, many studies have reported that pain is often managed inadequately because we tend to underestimate their cancer pain. The aim of this study was to evaluate the effectiveness of self-assessment of pain intensity for inpatients by means of a self-reported pain board. A self-reported pain board using self-moving indicators, which represents 0-10 numeric rating scales(NRS) and the frequency of breakthrough pain, was distributed on the bedside for 3 days. Thirty consecutive inpatients admitted in the Oncology Department of Chungbuk National University Hospital were included in this observational prospective study from February 2011 to June 2011. The self-reported pain board improved medical staff`s attitudes that the reliability of patients` pain increased from 59.4% to 76.1%. Patients` reliability over medical staff`s confidence of one`s pain increased from 77% to 99%. The NRS gap between patient and matched medical staff decreased from 2.47 to 0.77 after applying the self-reported pain board. The dose of morphine(mg/day/patient) for continous pain control increased from 71.8 to 92.7. As a result, the level of patients` satisfaction with pain management increased from 50% to 66.7%. Moreover, the work load of medical staff to assess the patients` pain decreased from 46.4 to 24.3. We suggest that the self-reported pain assessment tool is a reliable and effective instrument for inpatient cancer pain assessment.