In this study Mentofin (R) was used in commercial broiler chickens naturally exposed to infectious bursal disease virus ( IBDV) and administered live Newcastle disease virus (NDV) vaccine to evaluate the ability of Mentofin (R) to reduce Escherichia coli-related respiratory lesions, immunomodulate Newcastle disease (ND) vaccine response, change pharyngeal aerobic bacterial counts, and have certain impacts on specific production parameters. Mentofin (R) was added to the drinking water ( 100 ml/500 l water) of broiler chickens aged between 3 and 5 days. ND and IBD vaccinations were administered via drinking water to 15-day-old chickens. NDV vaccination was given again when the chickens were 20 days old. No difference was found between the control and Mentofin (R) groups regarding oropharyngeal aerobic bacterial counts. Acute IBD was diagnosed in both groups because the antibody levels were unprotective and varied widely. The mean NDV-hemagglutination inhibition antibody titers obtained with NDV vaccination in both groups were above the protective level, and the titers were considered uniform. The data showed that Mentofin (R) was able to reduce the lesions caused by E. coli after NDV vaccination. Mentofin (R) also reduced the rate of mortality in broilers with IBD interaction to the live NDV. In conclusion, Mentofin (R) reduced both the occurrence of E. coli-related lesions and the mortality rate usually observed after administering live NDV to broilers with clinical IBD.