To provide a roller bearing assembly, which can be assembled with a minimized number of assembling steps and without any drop-off preventing sleeve being employed and which can provide a large load bearing capacity, the roller bearing assembly includes an inner race 1 having a raceway surface 1a defined therein, a plurality of rollers 2, and a ring-shaped roller retainer 3 having a plurality of pockets 4 defined therein in a direction circumferentially thereof for accommodating therein the respective rollers 2 in a circular row. The roller retainer 3 also has pillars 5 each defined between the neighboring pockets 4. The roller retainer 3 is positioned on the inner race 1 with each of the pillars 5 thereof intervening between the neighboring rollers 2 to thereby retain the rollers 2 in position within the respective pockets 4 from a direction radially outwardly of the row of the rollers 2. The diameter of the circle depicted by and in touch with the pillars 5 is chosen to be greater than the diameter of the pitch circle PCD depicted in the circular row of the rollers 2.