A blade server system is described. The blade server system includes a main chassis, a rear module chassis and a mid-plane. The main chassis is formed with slots into which a plurality of sever blades are slidablely inserted from the front end of the main chassis. The rear module chassis is removablely mounted to the rear end of the main chassis, and divided into plural partitions for housing different component modules. The mid-plane is mounted to an end of the rear module chassis, and includes a first face and an opposite second face. The first face has plural connectors electrically connected to the server blades and the second face has plural connectors electrically connected to the component modules. Therefore, when maintenance is needed for the mid-plane, the service engineer only needs to withdraw the entire rear module chassis as a whole, without the need to remove the individual component modules.