A method and an apparatus for starting a vehicle engine are provided to improve compatibility between an immobilizer system and an engine control unit, by judging the type of the immobilizer system and setting a communication protocol between the immobilizer system and the engine control unit in accordance with the result of the judgment. A method for starting a vehicle engine, comprises a step(100 to 103) of receiving a key code supplied from a start key of a vehicle through an engine control unit, and initializing the engine control unit; a step(105 to 115) of judging whether the key code is received through an interface unit, judging as a first immobilizer system for executing authentication and password matching for the received key code and storing the result of the judgment if the key code is received through the interface unit, and judging whether the key code is matched, through an authentication module and a password module and controlling engine start; and a step(119) of judging as a second immobilizer system for executing password matching for the key code if the key code is not received through the interface unit, and judging whether the key code is matched, through a password module of the engine control unit and controlling engine start.
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