Abstract: A cell phone case audio amplifying device includes a cell phone case. The cell phone case has a sound wave guiding duct or a sound wave guiding trench corresponding in position to an audio outlet of a speaker of a cell phone. The sound wave guiding duct opens at two ends thereof and widens gradually while extending lengthwise to thereby amplify sound at least threefold. A sound wave outlet is disposed on a lateral side of the cell phone case. The sound wave outlet is in communication with a largest opening side of the sound wave guiding duct. The sound wave outlet enables the amplified sound to propagate to the outside efficiently, such that the cell phone case is capable of audio amplification.