Pope Sylvester III or Silvester III (c. 1000 – 1062 or 1063), born Giovanni dei Crescenzi–Ottaviani in Rome, was Pope from 20 January to March 1045.

When Pope Benedict IX was driven from Rome in September 1044, John, bishop of Sabina, was elected after fierce and protracted infighting. He took the name Sylvester III in January 1045. Benedict IX issued an excommunication of the new Pope and in March returned to Rome and expelled Sylvester, who himself returned to Sabina to again take up his office of bishop in that diocese.