The Turkish champions started with Jankat Yılmaz in goal, alongside Eren Elmalı, Kaan Ayhan, Abdulkerim Bardakcı, Arda Unyay, Kazımcan Karataş, Roland Sallai, Lucas Torreira, İlkay Gundogan, Yunus Akgun and Victor Osimhen.
The game remained goalless at half-time before Venezia took control and scored three times, including one goal from the penalty spot.
Galatasaray also missed a penalty and struck the post during the contest. Several players, including Barıs Alper Yılmaz, Victor Nelsson, Lesley Ugochukwu, Gabriel Sara and Elias Jelert, were introduced after the break.
Galatasaray will now continue preparations for their next friendly against Rennes at Rams Park.
