The purposes of this study were (1) to examine the psychometric properties of the Taiwanese version of the Morisky Medication Adherence Measure (MMAM), including its validity and reliability, (2) to investigate levels of analgesic regimen adherence, and (3) to explore the predictors of adherence to the analgesic regimen in a sample of Taiwanese cancer patients with pain. One hundred thirty-five patients receiving analgesics for cancer pain participated in this study. Instruments consisted of the Taiwanese version of the MMAM, the Barriers Questionnaire-Taiwan form, the Chinese version of the Brief Pain Inventory, the American Pain Society Outcome Questionnaire, Karnofsky Performance Status, and a demographic questionnaire. Analgesic use ratios were calculated. The Taiwanese version of the MMAM had good psychometric properties for measuring adherence with the analgesic regimens taken by Taiwanese cancer pain patients. Reliability was supported by good internal consistency Cronbach alpha and test-retest coefficients. Validity was corroborated by good known group validity, construct validity, and criterion-related validity. The majority of the patients (51%) showed low levels of medication adherence. The significant predictors for the medication adherence score were age, the Barriers Questionnaire score, and satisfaction with pain management by clinicians after entering pain severity, pain interference with daily life, age, gender, education, types of analgesics used, functional status, and satisfaction with pain management as independent variables. The model accounted for 63% of the variance in the medication adherence score. The Taiwanese version of the MMAM shows excellent reliability and validity. The use of this reliable, valid, simple, and easily administered tool can improve communication between patients and clinicians about use of analgesics and further improve the analgesic regimen adherence.