An OLED display substrate and a display panel are provided. The OLED display substrate includes: plural display regions and a spacer region separating the plural display regions from each other, each display region having plural pixel units disposed therein, and each pixel unit including plural OLED devices respectively emitting light of different colors; a first cathode connection line and an insulating layer disposed in at least one display region and sequentially disposed between a base substrate and the plural OLED devices, cathodes of all OLED devices located in a same display region having a one-piece structure; a via hole arranged in the insulating layer, the cathodes of all OLED devices located in the same display region being connected to the first cathode connection line through the via hole; and a second cathode connection line disposed in the spacer region and connected to the first cathode connection line.