Defensive lineman Leonard Williams, linebacker Hayes Pullard and safety Su'a Cravens were selected along with receiver Nelson Agholor.
Williams has been selected to several preseason All-America teams and is regarded as a potential NFL first-round draft pick. Last season, he had 13 1/2 tackles for losses, including six sacks.
Pullard, a senior, is a returning team captain and the most experienced player on defense. Last season, he had a team-best 94 tackles.
Cravens, a sophomore, intercepted four passes and was a freshman All-American in 2013.
Agholor caught 56 passes, six for touchdowns, last season. He also returned two punts for touchdowns.
USC opens Aug. 30 against Fresno State.