A memory storage device having a rewritable non-volatile memory module, a first connection interface unit, a second connection interface unit, a power management circuit and a memory control circuit unit is provided. When an external power supply device is electrically connected to the second connection interface unit, the power management circuit receives a second power supply voltage from the external power supply device via the second connection interface unit, supplies an operation voltage to the rewritable non-volatile memory module and the memory control circuit unit and supplies the second power supply voltage to a host device. When the external power supply device is electrically disconnected with the second connection interface unit, the power management circuit receives a first power supply voltage from the host device via the first connection interface unit and supplies the operation voltage to the memory control circuit unit and the rewritable non-volatile memory module.