Particle classifier (2) for separating solid particles in a flow of gas and particles (1) into two fractions depending on size by means of gravitation force, air resistance force and applied centripetal force. A mixture of gas and particles is charged well dispersed to a classifier inlet zone (3) from which the mixture is brought into contact with a rotor (6) in a first separation zone (5) having the form of a free rotor chamber. Gas and fine particles are allowed to escape through an upper outlet (9) while the coarse fraction of the particles is forced to pass through a second separation zone and subsequently to leave through a lower outlet (15). Vertically below the first separation zone (5) a second separation zone having the form of an annular chamber (11) is arranged, radially outwards delimited by stationary vanes (12) that are interspaced circumferentially around the rotor, the distance between the rotor periphery and said stationary vanes being less than the distance between the rotor periphery and the wall (7) of the classifier's first separation zone (5).