Human gastrointestinal tract harbors trillions of microbes to form the gut microbiota. Through interacting with host cells, gut microbes play critical roles in host physiology and function. Immunotherapy has risen as a promising means to fight cancer. Studies have revealed the close association of gut microbiota with immunotherapy efficacy. Investigations on the relationship between microbiota and immunotherapy can have important clinical significance, potentially leading to the development of more effective cancer therapeutics.