This study was done to evaluate the effectiveness of premedication with simethicone or N- acetylcysteine (NAC) on enhancing endoscopic visibility in patient undergoing Esophagogastroduodenoscopy. This was a Randomized Double –blind Clinical Trial. The study included 350 children, ranged in age from 6 months to 15 years. patients were randomly allocated into three groups to receive one of the following premedications (: group 1 : Placebo, group 2: N- acetylcysteine, group 3: simehticone) with 10 ml of water at 20 minutes before Esophagogastroduodenoscopy .It was rated the amount of foam and air bubbles ,and divided into four degrees from 0 to3 degree, The scores of foam and air bubbles were compared and the duration of endoscope also compared between the three groups. The amount of foam/air bubbles was significantly lower in the simeticone group compared with the placebo and NAC group (p 0,0001) The duration of endoscopy was shorter in the simeticone group (P 0,0001)