A process to perform the finishing of polyolefins produced by gas-phase catalytic polymerization of one or more alpha-olefins in the presence of a polymerization diluent selected from a C3-C5 alkane, wherein the polyolefm granules discharged from the gas-phase reactor are subjected to: (1) a first degassing step in which said polyolefm is counter-currently contacted with a gaseous stream containing at least 85% by mol of a stripping agent selected from a C3-C5 alkane, said gaseous stream being continuously derived from the monomer recovery section of the polymerization plant; (2) a second degassing step in which said polyolefin is counter-currently contacted with steam, the amount of steam being from 10 to 200 Kg per 1000 kg of polyolefin.