The present invention refers to a new polymorph of Rufinamide, designed as Form R-5, the process for obtaining it, the composition containing it and its use as medicament.The new polymorph of Rufinamide shows good stability and appropriate physico-chemical properties for its manipulation on industrial scale. Polymorph Form R-5 will be suitable to use as pharmaceutical for the treatment of convulsions, especially for the treatment of epilepsy.