Provided is a battery pack, which can increase coupling force between a holder and a protection circuit board, and improve processability and productivity. The battery pack includes a bare cell, a holder disposed at one side of the bare cell and having a first fastening part, and a protection circuit assembly disposed at one side of the holder and having a second fastening part coupled to the first fastening part, wherein one of the first and second fastening parts is a protrusion and the other is a groove, and the protrusion includes a first supporting surface, a second supporting surface and a notch formed between the first and second supporting surfaces. Also, the battery pack includes a bare cell, a holder disposed at one side of the bare cell and having a first fastening part, and a protection circuit assembly disposed at one side of the holder and having a second fastening part coupled to the first fastening part, wherein the first fastening part is a first protrusion and the second fastening part is a second protrusion, and one of the first and second protrusions includes a first supporting surface, a second supporting surface and a notch formed between the first and second supporting surfaces and the other is formed in the shape of a square pillar.