The present invention discloses a data processing device and a motherboard thereof. The feature of the present invention is separating the motherboard thereof into two daughter boards. The first daughter board is fixed to the data processing device, and the second daughter board is connected to the first daughter board through a connector. The units that frequently be changed, such as a data processing component and data storing component, are disposed on the second daughter board. Besides, a hard disk signal bus of the data processing device, an optical disk drive signal bus, or a screen signal bus may be electrically connected to the first daughter board. As a result, when the data processing device is under maintenance or upgrade, the second daughter board can be removed without removing the casing, and also the plug-in and plug-out frequency of the connectors can be lower.