Process for producing graphene nanoplatelets, comprising expanding flakes of intercalated graphite and collection of the same in a dispersing medium with forming of a dispersion that is subjected to exfoliation and size reduction treatment carried out by high pressure homogenization in a high shear homogenizer. A dispersion of graphene is obtained in the form of nanoplatelets, at least 90% of which have a lateral size (x, y) from 50 to 50,000 nm and a thickness (z) from 0.34 to 50 nm.