A method for determining causes of engine stop using ignition power monitoring may include performing ignition power holding determination to determine, in a state in which a vehicle is started and an engine is driven, whether the vehicle is in a key-on state, to which power is consistently applied, in order to hold the starting of the engine of the vehicle. The method also includes performing power-off recognition time comparison by comparing, when ignition power is turned off and the engine is stopped, a time required to recognize ignition power-off in an ECU (Electronic Control Unit) with a preset ignition power-off recognition time for failure determination. The method also performs a power abnormality determination by determining whether the engine is stopped due to ignition power failure when the time required to recognize the ignition power-off in the ECU is not greater than the preset ignition power-off recognition time.