The objective of this review is to summarize the effect of commonly used mushrooms (particularly Pleurotus ostreatus or oyster mushroom, Agaricus bisporus or Button mushroom, Lentimula edodes or shiitake mushroom, and Ganoderma lucidum or reishi mushroom) in poultry diets on performance of broilers and layers. It can be concluded from different studies that mushrooms and their polysaccharides can play important roles in poultry production: (1) Polysaccharides in mushrooms may act as immune enhancers or immunomodulators and show antibacterial, antiviral, antiparasitic bioactivities; (2) phenolic compounds of mushrooms may act as antioxidants; (3) mushrooms in broiler's diet may be used as growth promoters as an alternative to antibiotics; (4) mushrooms in the diet may improve egg production and quality; (5) mushrooms may be used as a safe and effective alternative for inducing molt, enhancing immunity, reducing Salmonella growth, and returning to egg production. Further studies are needed to investigate the effects of mushrooms to improve productive performance in chickens and to illuminate the possible modes of action related to the gut ecosystem and the immune response. [ABSTRACT FROM AUTHOR]