Mobile electronic device capable of switching user interfaces and method thereof

A mobile electronic device includes a storage unit, a display module, an audio speaker module, a sound receiving module and a control unit. The storage unit is for storing at least one character data. The display module is for selectively displaying a first user interface or a second user interface. The audio speaker module is for playing a voice. The sound receiving module is for receiving the voice played by the audio speaker module. The control unit is coupled to the storage unit, the display module and the sound receiving module. The control unit is for generating a character signal corresponding to the voice and controlling the display module to switch from the first user interface to the second user interface when determining the character signal matches the at least one character data.