Disclosed herein is a battery pack including an electrically insulative pack case. The battery pack includes a plate-shaped battery cell having an anode terminal and a cathode terminal formed at one side thereof including a sealed surplus portion, the battery cell being formed to have a planar quadrangular structure, a protection circuit module (PCM) electrically connected to the electrode terminals of the battery cell to control operation of the battery pack, the PCM being loaded on the sealed surplus portion of the battery cell, and a pack case applied to the sealed surplus portion of the battery cell, the PCM, and opposite sides of the battery cell in a thermally molten state and solidified, the pack case being configured to have a structure to cover the sealed surplus portion of the battery cell, the PCM, and the opposite sides of the battery cell in a state in which the top and bottom of the battery cell are open.