The present invention provides a universal serial bus (USB) voltage transformer, which comprises a main body, a transformer circuit unit, and several connectors. The transformer circuit unit is disposed in or at the inside of the main body. The connectors are electrically connected to the transformer circuit unit directly or via a connection cable. A USB voltage transformer having travel charging function is thus formed. The USB voltage transformer of the present invention can simultaneously charge several portable electronic devices like mobile phones, personal digital assistants, electronic translators, and small cameras.