Abstract: For the trade-off of performance, power and compatibility, core circuits and I/O circuits of chips generally use different power supply.This article designs a novel 2.5V/5V double-power supply output circuit with a novel level converter, which can convert the interior signal between 0 and 2.5V to the exterior signal between 0 and 5V.Moreover, the output circuit which uses only thin gate-oxide MOS devices enduring 2.5V power supply can operate in the 5V power supply, and doesn't have the problem of gate-oxide overstress.