Pluto Kuiper Express was an interplanetary space probe that was proposed by Jet Propulsion Laboratory (JPL) scientists and engineers and under development by NASA. The spacecraft was intended to be launched to study Pluto and its moon Charon, along with one or more other Kuiper belt objects (KBOs). The proposal was the third of its kind, after the Pluto 350 and a proposal to send a Mariner Mark II spacecraft to Pluto.

Originally conceived as Pluto Fast Flyby, and later briefly named Pluto Express, the mission was inspired by a 1991 United States Postal Service stamp that branded Pluto as "Not Yet Explored". The project brought on JPL engineers and students from the California Institute of Technology and, later, Alan Stern and other scientists from the Pluto 350 project. While the project was initiated in 1992, the project's development phase was lengthy, spending nearly a decade in the proposal and funding stage. During planning, the mission was changed to include a Kuiper belt object flyby and re-christened the Pluto Kuiper Express, after the discovery of numerous such objects beyond Neptune in the mid-to-late 1990s. NASA ultimately decided to cancel the mission in 2000, however, citing the project's expanding budget as the ultimate reason for the cancellation.

After the mission's cancellation, most of the Pluto Fast Flyby team, including Stern, went on to develop New Horizons, a mission nearly identical to Pluto Kuiper Express, for NASA's New Frontiers program. The spacecraft was successfully launched in January 2006, after a financial standoff with NASA and additional delays, and went on to perform the first ever flyby of the Pluto-Charon system in July 2015.