The 27-year-old Italy captain, who has 64 international caps, impressed in his debut season with the Guinness Premiership side last year after switching from Narbonne.
Bortolami said: "Gloucester is my new home, my new life and my passion - for me to be able to stay for another two years is fantastic.
"We made great progress last season, and now it is up to us to build on it and create something very special in Gloucester's history.
"I believe in what we are trying to achieve and in Dean Ryan's philosophy for the team. We are young; we are ambitious - and we want to be successful."
Ryan himself said: "When Marco arrived at the club from Narbonne we believed he had the qualities to become a world-class second row - not only as a player but also as an individual - and it delights me we have such a player within our squad."
Bortolami joins Alex Brown, Andy Hazell, James Simpson-Daniel and Will James in pledging their futures to Gloucester since the beginning of the season.
Ryan added: "We are trying to build something that will create a legacy at Gloucester, and Marco is central to that. I am absolutely delighted we have extended his contract."