A self-locking structure of a split roller bearing cage includes recesses, locker plates and locking projections. The recesses are defined in outer circumferential surfaces of opposite joint ends of two semicircular split roller bearing cage half-parts along horizontally inscribed tangential lines, that meet an outer circumference of the annular split roller bearing cage and intersect perpendicular with a split center axis of the annular split roller bearing cage. Recesses have widths and depths suitable to receive locker plates. The locker plates are horizontally attached to bottoms of the recesses defined in opposite joint ends of one of the cage half-parts. Locking projections are formed at bottoms of other recesses defined in opposite joint ends of the other cage half-parts to be coupled with respective locker plates. The two cage half-parts are aligned and engaged at their joint ends, forming a full circle. The locker plates can be automatically coupled to the locking projections.