This is a multi-centre, randomized, open-label, flexible-titration, controlled, parallel-group study to investigate the safety and efficacy of a novel modified release formulation of oxcarbazepine (OXC MR) compared to an immediate release oxcarbazepine (OXC IR) product in patients with partial epilepsy. Adult patients of both gender, aged at least 18 years with refractory partial epilepsy, with or without secondary generalisation receiving a stable background treatment with daily dosages of exactly 900 or 1200 or 1500 mg Oxcarbazepine will be enrolled. Concomitant medication consisting of maximal 2 additional AEDs (vagus nerve stimulator included) is allowed and must be kept stable throughout the study. Patients, who agree to participate, will first sign and date the informed consent and undergo an evaluation at screening visit to determine eligibility. Those patients who qualify will be enrolled in the study, assigned a patient ID, and will enter the 4-week baseline period. Each patient will receive a seizure diary to record the number of seizures during the baseline period. For Visit 1 the patient will return to the clinic and complete all baseline procedures. Patients who have met the entry criteria will be randomised. The two treatment groups consist of 50 patients each, one group to be treated with OXC MR b.i.d. and the other to be treated with OXC IR b.i.d. in a 1:1 randomization. Following assignment to one of both treatment groups the patient will enter the dose-titration phase. From Visit 1 (Study Day 1) a total daily dose of 1200 mg /1500 mg /1800 mg oxcarbazepine will be given to the randomised patients. From Day 6 the dosage will be titrated to a maximum total daily dose of 2700 mg in steps of 300 mg every 6th day. Patients who experienced intolerable adverse events could reduce their daily dose by 150 mg on the 2nd day of up-titration for the remainder of the treatment period. In case the reduced dosage will also not be tolerated, in a second step the dosage can be reduced by further 150 mg OXC. The maximal tolerated dose achieved on up-titration will be maintained up to the final visit (Study Day 26).