كتب : Hatem Maher
The Egyptian striker was introduced in seven minutes past the hour mark when Bolton were leading 2-0.
Kevin Davies put the visitors ahead after 10 minutes when he headed home a pinpoint cross from Lee Chung-Yong.
Jack Wilshere, who is on loan from Arsenal, doubled their advantage six minutes later to leave West Ham with a mountain to climb.
Mido replaced Mexican striker Guillermo Franco as the Hammers coach Gianfranco Zola sought to add much-needed impetus upfront.
But the 27-year-old hardly made an impact, failing to open his account with the team he joined in January on loan until the end of the season.
Bolton's Tamir Cohen was sent off in the 70th minute for a second bookable offense, giving West Ham the chance to narrow the gap two minutes from time.
Italian attacking midfielder Alessandro Diamanti curled a superb shot past the keeper but Bolton held on for their first away victory since September.
West Ham, who lost 3-0 to Manchester United in their previous game, lie 14th in the 20-team league table with 27 points, just three above the relegation zone.