Chemotherapeutic agents, especially paclitaxel, and endocrinotherapeutic agents such as aromatase inhibitors and antiestrogen, can induce seriously painful symptoms in breast cancer patients during adjuvant treatment before and after surgery. We report five clinical cases in which oxycodone was effective against pain induced by anti-cancer agents during adjuvant treatment. Paclitaxel was used as the anti-cancer agent in each of the five patients. Aromatase inhibitors and anti-estrogen were administered to one and three patients, respectively. The daily dose of controlled-release oxycodone ranged from 10 mg to 270 mg, but none of the patients dropped out due to adverse events caused by oxycodone. Pain intensity measured by NRS decreased to less than 3 out of 10, compared to the baseline in every patient except for one. Oxycodone may be effective against anti-cancer agent-induced pain. In addition, appropriate assessment and management of pain may be crucial for breast cancer patients during adjuvant treatment.