The 49-year-old coach was dismissed after just 10 months in charge following Saturday's 1-0 defeat at Bristol City -- Reading's fifth loss in their last six league games.
"Following just two wins in the first 11 league games in 2019-20, owner Mr Yongge Dai has made the difficult decision to part company with Gomes and make a change at first-team level," Reading said in a statement.
Appointed in December, Portuguese coach Gomes led Reading to a 20th place finish last season as they successfully battled to avoid relegation.
Gomes was backed in the transfer market by Reading's Chinese owners, with seven new players signed during the summer window.
But he becomes the third managerial departure from the Madejski Stadium in 19 months, following Jaap Stam and Paul Clement.
Reading will use the international break to start the search for a new manager, with former Manchester City and Southampton boss Mark Hughes among the early favourites with the bookmakers.
Gomes is the third Championship boss to part ways with his club over the last week following second bottom Barnsley's sacking of Daniel Stendel and Neil Harris' decision to resign at Millwall.