In December 2011, Gentile left Treviso Basket and signed a four-year deal with Olimpia Milano.
In 2013–14, Gentile had a break-out season, averaging 11.4 points, 2.4 rebounds and 2.3 assists over 21 games in the EuroLeague.
In June 2014, after Milano won their 26th Italian League championship, Gentile was named the Italian League Finals MVP.

In July 2014, Gentile penned a new three-year contract with Milano.
A year later in 2015, the Milano captain extended his contract until 2018, with a new three-year deal.
On October 6, 2015, Gentile played against the NBA's Boston Celtics, in the NBA Global Games tournament.

Gentile was sent on loan to the Greek club Panathinaikos in December 2016.
However, Milano retained his rights through the 2017–18 season.
He was released by Panathinaikos in March 2017, and he finished the 2016–17 season by playing on loan for Hapoel Jerusalem in the Israeli Super League, and preparing for the upcoming EuroBasket 2017 tournament.
In December 2011, Gentile left Treviso Basket and signed a four-year deal with Olimpia Milano. In 2013–14, Gentile had a break-out season, averaging 11.4 points, 2.4 rebounds and 2.3 assists over 21 games in the EuroLeague. In June 2014, after Milano won their 26th Italian League championship, Gentile was named the Italian League Finals MVP.
In July 2014, Gentile penned a new three-year contract with Milano. A year later in 2015, the Milano captain extended his contract until 2018, with a new three-year deal. On October 6, 2015, Gentile played against the NBA's Boston Celtics, in the NBA Global Games tournament.
Gentile was sent on loan to the Greek club Panathinaikos in December 2016. However, Milano retained his rights through the 2017–18 season. He was released by Panathinaikos in March 2017, and he finished the 2016–17 season by playing on loan for Hapoel Jerusalem in the Israeli Super League, and preparing for the upcoming EuroBasket 2017 tournament.
Alessandro Gentile