Secondo Campini (born August 28 1904 in Bologna, died February 7 1980 in Milan) was an Italian engineer and one of the pioneers of the jet engine.

In 1931 Campini wrote a proposal for the Italian Air Ministry on the value of jet propulsion and in 1932 demonstrated a jet-powered boat in Venice. With support of the Air Ministry, he began work with Italian aircraft manufacturer Caproni to develop a jet plane, the Campini Caproni CC.2, which first flew in 1940.

The "Thermojet" that Campini developed to propel this aircraft is substantially different from the jet engines of today. Campini's engine used an ordinary piston engine to compress air which was then mixed with fuel and ignited. Modern jets are based on the turbojet principle, but Campini's jet was nevertheless a true jet, since it was the reactive force of the burning exhaust gases that pushed the plane along.

After World War II, Campini went to work in the US. Beginning in 1948, he worked on a number of military projects including the YB-49 flying-wing bomber.