The gut is a fundamental organ system which makes up two equally important functions, i.e., the digestion and host defence. To elicit the well-functioning and healthy gut, the dynamic balance of gut ecosystem is of importance. A wide range of factors related to diets and infectious disease agents seem to affect this balance, and subsequently affect the health status and production performance of the chicken. With the ban and/or reduction of the use of antibiotic growth promoters (AGPs) in poultry production, the alternatives to AGP are needed especially to preserve the balance of gut microbiota in chicken. This review provides a summary of the potentials and possible mechanisms of action of some alternatives to AGP (referred as nutraceuticals) in improving the gut microbial ecosystem and immune system as well as growth performance of poultry.