S55 may refer to:
Aircraft Savoia-Marchetti S.55, an Italian flying boat Sikorsky S-55, an American helicopter Sukhoi S-55, a proposed Russian fighter aircraft
Automobiles BMW S55, an automobile engine Mercedes-Benz S 55 AMG, a luxury car Mercury S-55, an American full-size car Shorland S55, a British armoured personnel carrier
Rail and transit S55 (New York City bus) serving Staten Island, United States S55 (ZVV), a former line of the Zurich S-Bahn in Switzerland S55, a former railway line in the canton of Thurgau, Switzerland, subsumed into the S5 (St. Gallen S-Bahn) S55, a line of Lucerne S-Bahn in Central Switzerland FGC line S55, a suburban train line in Catalonia, Spain
Other uses S55 (star) in the constellation Sagittarius Ariel 1, a British satellite County Route S55 (Bergen County, New Jersey) Explorer S-55 (satellite), a failed American spacecraft , a submarine of the Indian Navy Siemens S55, a mobile phone Wandandian language