An active device array substrate includes a flexible substrate, a gate electrode, a dielectric layer, a channel layer, a source electrode, a drain electrode, and a pixel electrode. The flexible substrate has a transistor region and a transparent region adjacent to each other. The gate electrode is disposed on the transistor region. The dielectric layer covers the flexible substrate and the gate electrode. A portion of the dielectric layer disposed on the gate electrode has a first thickness. Another portion of the dielectric layer disposed on the transparent region has a second thickness less than the first thickness. The channel layer is disposed above the gate electrode. The source electrode and the drain electrode are electrically connected to the channel layer. The pixel electrode is disposed on the dielectric layer which is disposed on the transparent region. The pixel electrode is electrically connected to the drain electrode.