A plant (1) for drying and solid state polycondensing a moisture-containing polymeric material (M) in granular form, comprising a conduit (2) for feeding the material to be treated in a longitudinal direction (L), at least one treatment zone (7) for treating the polymeric material, means (6) for blowing an inert gas into the conduit, radiating means (8) for emitting an alternating electromagnetic field in the radio-frequency band and comprising a plurality of applicators (9) located in correspondence of said treatment zone and external to the conduit in longitudinally offset positions; said applicators are connected to the terminals of an electromagnetic wave generator (10) and comprise pairs of opposed radiating elements (11, 11') which are adapted to generate an alternating electromagnetic field in the conduit; the pairs of radiating elements defining magnetic dipoles with opposite polarities along the conduit. Further claimed is a method of drying and solid state polycondensing a polymeric material in granular form obtained by polycondensation using the plant.