Abstract: A high-frequency and high-voltage power supply unit with an internal protecting circuit includes a first DC power supply device, a second DC power supply device, a converting circuit, a sensing/holding circuit, and an amplifying circuit, where the DC power supply device incorporates with the converting circuit to generate high-frequency and high-voltage power to a neon light load. A wire is connected between a core of a third transformer and the sensing/holding circuit, and a pair of discharging tips disposed between the wire and one output terminal, such that when both output terminals disconnect from the load, a discharge occurs on the dischraging tips, causing an impulse which is further fed back to the sensing/holding circuit through the amplying circuit cutting off the operation of the converting circuit.