The present invention relates to a process of preparing solid oral modified-release composition comprising oxcarbazepine or salts thereof. In particular, the process involves a step of preparation of a matrix of oxcarbazepine or salts thereof with one or more rate-controlling excipients having pH independent solubility; wherein the composition is devoid of excipients having pH dependent solubility. The invention further provides a method of treatment of epileptic seizures.