Fiber-reinforced polymer compositions containing resin components including (a) 30-90 weight % of polyamide resins, and (b) 10-70 weight % of polyolefins + unsaturated carboxylic acid-modified polyolefins, based on the resin components; and (c) 5-50 parts by weight of glass fibers per 100 parts by weight of the total compositions, a molar ratio of end amino groups in the polyamide resins to carboxyl groups in the modified polyolefins being 10-1000. The compositions have a morphology in which polyolefin domains having an average size of 0.5-5 pm are uniformly dispersed in polyamide matrix phases. The are produced by a double-screw extruder having a length/inner diameter (L/D) ratio of 25 or more and having a first hopper (1) for introducing the resin components, a second hopper (3) for introducing the glass fibers, a vent (4) and a die exit (2) in this order, and further having at least one first kneading zone (5) for strongly kneading the resin components, and at least one second kneading zone (6) disposed between the second hopper and the vent for strongly kneading the resin components and the glass fibers.