This is an interventional, open label, randomized controlled study carrying in multi-centers. Eighty opioid-naive patients with moderate to severe cancer pain (≥ 4) in outpatient department (OPD), who agreed and signed informed consent will be randomly assigned in a 1:1 ratio to receive CR + IR oxycodone or conventional IR oxycodone groups. The study is to compare the titration efficacy and safety of CR with IR oxycodone (experimental group) comparing IR oxycodone (control group) in cancer patients suffered with moderate to severe pain. The study last 14 days. Patients begin the study by the first day visit of the clinic and received the study medication (Baseline). Following visits on cycle 1 (day 3 or 4 depends on the available clinics), cycle 2 (day 7±1), cycle 3 (day 10±1), and cycle 4 (day 14±1). In the experimental group, 10 mg CR oxycodone tablet will be selected as background dose of titration, and patients will be administered once every 12 hrs. Meanwhile, the titration with IR oxycodone will be added according to the pain intensity, e.g. if patient receiving 6 tablets of 10 mg CR oxycodone (giving in Q12H frequency for 3 days), 12 capsules of 5mg IR oxycodone will be dispensed for managing acute pain (rescue use) for the first cycle. In the control group, the conventional titration with IR oxycodone will be conducted according to pain intensity, using 5 mg as initial dose, e.g. 12 capsules of 5mg IR oxycodone (giving in Q6H frequency for 3 days), 12 capsules of 5mg IR oxycodone will be dispensed for rescue use upon to the first cycle. Patient will record their pain score (4 times in Q6H frequency and before taking the drug), 24hr total dose (total tablets/capsule number), number of breakthrough pain and PRN time and dosage used onto the patient diary. The background dose of each patient will be titrated after cycle 1 by investigators. Titration cycles will be recorded and evaluated pain assessments on cycle 2 (day 7±1), cycle 3 (Day 10±1), cycle 4 (day 14±1). During study, the study nurse will follow patient's daily records, drug use condition every second day by telephone or other contact methods to keep close monitor of patient's condition. The telephone contact for cycle 1 and cycle 3 is acceptable for this study. If the telephone contact is conducted for patient, the 1-week quantities of oxycodone should be dispensed to patient.