Objective: Sodium phosphate is an agent used in bowel preparation for colonoscopic examination. However, the intraluminal gas can impair visibility during the procedure. Simethicone is effective in reducing the surface tension of air bubbles. The present study was aimed at evaluating the effectiveness of simethicone in enhancing visibility during colonoscopy.Methods: A prospective, randomized, double-blinded, placebo-controlled study was conducted. One-hundred- t test or Chi-square test as appropriate. Results: presence of symptoms in 58.2% and for screening purpose in 41.8% of cases, respectively. Colonoscopic findings were normal in 27.1%, polyps in 48.4% and cancer in 3.3%. Total colonoscopy was not achieved in 2 patients (1 from each group). Sodium phosphate plus simethicone improved visibility by diminishing air bubbles than sodium phosphate plus placebo (100% vs 42.37%, haziness compare to sodium phosphate plus placebo (90.16% vs 81.36%, satisfaction were both higher in the sodium phosphate plus simethicone group (79.03% vs 32.76%, vs 7.6 ± 1.9, of colonoscopy (25.1 ± 13.1 vs 27.3 ± 12.9 minutes) and the side effects score of medication (1.39 ± 2.3 vs 1.76 ± 2.2). Demographic data in the two groups were comparable. Colonoscopy was performed because ofp <0.0001). However, sodium phosphate plus simethicone failed to demonstrate diminishingp = 0.17). Endoscopist satisfaction and patientp <0.0001 and 8.7 ± 1.8p = 0.002, respectively). However, there was no difference between the 2 groups regarding the total duration Conclusion: bowel preparation. Simethicone diminished air bubbles, resulted in enhancing visibility and improving the quality of colonoscopy. Endoscopist satisfaction and patient satisfaction were also greater with sodium phosphate plus simethicone. The addition of simethicone to sodium phosphate was shown to be useful for colonoscopic  and-twenty-four patients were allocated to receive either 45 ml of sodium phosphate plus 240 mg of simethicone tablets or 45 ml of sodium phosphate plus an identical placebo given first in the evening before and again in the morning of the examination. The entire procedure was recorded. Visibility was blindly assessed by a single investigator based on the amount of air bubbles and the degree of haziness. Five areas of the colon were graded for the amount of air bubbles from grade 0 to grade 3. Haziness was graded in 5 levels from excellent to unacceptable. Endoscopist satisfaction was evaluated by means of questionnaires. Visual analog scale (0-10) was used for rating patient satisfaction and side effects of medication. The total time taken or duration of colonoscopy, side effects of medication, endoscopist satisfaction and patient satisfaction were recorded and compared between the two groups. Data analysis was performed using student’s