Midfielder Ertl, who has also played for Crystal Palace and Sheffield United, moved to Fratton Park last August.
The 30-year-old Austrian made 39 appearances last season with his performances earning him the player of the year award.
He has now joined defender Dan Butler and strikers David Connolly and Patrick Agyemang in committing themselves to Pompey's bid to bounce back from relegation to League Two next term.
- Sports & Recreation
- Sheffield United
- Patrick Agyemang
- Fratton Park