To provide a roller bearing assembly that can provide a high load bearing capacity and in which the strength of roller retainers can be increased, the roller bearing assembly includes inner and outer roller retainers (13, 23) each having a plurality of circumferentially arranged pockets (4), and a circular row of rollers (2) received in part within the pockets in the inner roller (13) and in part within the pockets in the outer roller (23). The inner roller retainer (13) has pillars (5) each left between the neighboring pockets to retain the circular row of the rollers from radially inwardly and having an outer diameter smaller than the diameter of the pitch circle PCD of the circular row of the rollers. The outer roller retainer (23) has pillars (5) each left between the neighboring pockets to retain the circular row of the rollers from radially outwardly and having an inner diameter greater than the pitch circle diameter PCD. One of the outer and inner roller retainers is made of a metallic material while the other thereof is made of a resinous material.