In a high gradient magnetic separator with a separation zone consisting of a matrix of parallel magnetic wires arranged in parallel planes and channels formed by a non-magnetic material and extending in each plane between adjacent parallel magnetic wires for conducting a fluid including magnetic particles through the matrix, and a magnetizing structure disposed adjacent the matrix for generating a magnetic field with field lines which extend essentially normal to the parallel planes, separating walls are disposed in parts of the channels in the area ahead of the end of the magnetic field generated in the matrix and adjacent the flow exit end of the matrix so as to extend parallel to the planes and normal to the magnetic field lines and form partial flow channels receiving partial fluid flows of magnetic particle-enriched and, respectively, magnetic particle-depleted flow volumes.