A DC uninterruptible power supply apparatus with bidirectional protection function receives a DC power source and supplies power to a DC load. The DC uninterruptible power supply apparatus includes a first loop, a second loop, a third loop, and a control unit. The first loop receives the DC power source and supplies power to the DC load. The second loop converts the DC power source into an energy-storing power source to charge an energy-storing unit. The energy-storing unit provides a backup power source to the DC load through the third loop and the first loop. The control unit controls the first loop, the second loop, and the third loop to correspondingly provide a first protection mechanism, a second protection mechanism, and a third protection mechanism.