Background: Rapid loss of weight after bariatric surgery is associated with a high incidence of gallstone formation. This study was carried out to detect the efficacy of six months regimen of prophylactic Ursodeoxycholic acid in the prevention of gallstones and to identify the predictive factors for gallstone formation after weight loss surgery. Methods:  A  randomized  controlled  trial  was  carried  out  involving  108  patients  with a preoperative diagnosis of morbid obesity were subjected to either laparoscopic sleeve gastrectomy (LSG) or greater curve plication (LGCP) with follow-up for a minimum one year; they were divided into two groups; (group A; receiving Ursodeoxycholic acid) and (group B; receiving placebo). Data were collected about: Patient clinical history, baseline characteristics and postoperative follow-up. Results: The demographic parameters were comparable in the two groups. The incidence of cholelithiasis after surgery was 14.3% (13 cases). The mean %EWL was significantly higher in those who develop gallstones than others (P= 0.045). Also, there was a significant increased cholelithiasis post-LSG than LGCP (P=0.036). There was a significant decrease in the incidence of gallstone formation from 22% in placebo to 6.5% in treated group with Ursodeoxycholic acid (P = 0.041). Conclusions: The percentage of excess weight loss was the only predictive postoperative factor for gallstone formation. A six months use of Ursodeoxycholic acid is an effective prophylaxis for gallstone formation after weight loss procedures although a larger study is required to reach a definitive conclusion.