Background and Aims: Antispasmodics such as cimetropium bromide (CB) has been widely used as a premedication to facilitate upper gastrointestinal endoscopy (GIE). But the clinical benefit of CB was questioned with the instrumental and technical advancement of GIE. We performed this study to investigate the clinical usefulness of CB as a premedication for GIE. Methods: In this prospective, double-blind, randomized trial, 320 consecutive patients undergoing GIE (using Olympus GIF Type H260 or Q260, from September to November 2007) under conscious sedation with midazolam were enrolled and randomly allocated to receive either intravenous CB(CB group, n = 157) or intravenous normal saline (placebo group, n = 163). We measured the time required for GIE and the outcome parameters of CB by endoscopists during the procedure in each group. The outcome parameters, scored on a five-point scale, included (1) peristaltic activity score, (2) belching score, (3) difficulty to pass through the pyloric ring score, and (4) intragastric secretion score. Results: Baseline characteristics such as age (CB group: 46.0 ± 13.0, placebo group 44.3 ± 13.5; p = 0.251), sex (p = 0.951), and comorbidity (p = 0.125) in each group were well matched. The time required for GIE (2.26 ± 1.29 minutes in CB group, 2.87 ± 1.48 minutes in placebo group; p = 0.052) was similar. And there were no statistically significant differences between the two groups in all outcome parameters including peristaltic activity score (p = 0.827), belching score (p = 0.939), difficulty to pass through the pyloric ring score (p = 0.563), and intragastric secretion score (p = 0.475). Conclusion: This study shows that the use of cimetropium bromide as a premedication for GIE has no clinical benefit in terms of all parameters we used. Therefore, besides the cost of drug and labors, the routine use of cimetropium bromide as a premedication for GIE may be of little or no benefit in facilitating GIE.