The present application provides an organic light emitting display substrate and a method of fabricating the same. The organic light emitting display substrate includes: a base substrate; and a driving transistor provided on the base substrate, wherein the driving transistor includes: an active layer; a first insulating layer having at least one sub-layer covering the active layer and having a first via hole therein; and a source electrode and a drain electrode disposed on a side of the first insulating layer distal to the base substrate, and connected to the active layer through the first via hole in the first insulating layer.