Ertz, a finalist for the Mackey Award given to the nation's top tight end, led the Cardinal with 69 receptions for 898 yards and six touchdowns. He averaged 64.1 receiving yards per game.
Ertz, the top tight end and No. 29 overall player as rated by ESPN's Scouts Inc., was pivotal in helping Stanford to a 12-2 record, a Pac-12 championship and a 20-14 win over Wisconsin in the Rose Bowl.
Stanford's No. 2 tight end, junior Levine Toilolo, also announced Monday he will enter the draft. Toilolo finished with 24 receptions for 393 yards and four touchdowns this season.
"In light of achieving our collective dream of winning the Rose Bowl Game, it is difficult to imagine not playing side-by-side with my Stanford brothers for another season," Ertz said in a statement released through the school.
"However, after returning home and talking to my family, coaches and advisors and conducting a thorough analysis of the situation, I have decided to forego my final year of eligibility at Stanford University. It has been a dream of mine to play in the NFL for as long as I can remember, and I would not be in this position without my coaches, professors and everyone associated with the university."
In the statement, Ertz said he plans to graduate in June with a Bachelor of Science degree in management science and engineering.
In a recent chat session, ESPN.com's Mel Kiper Jr. projected Ertz as a potential second-round draft pick.
Information from ESPN's Joe Schad was used in this report.