Immunotherapy brings hope to cancer patients but the clinical outcome of cancer immunotherapy monotherapy or combined therapy is not ideal. Screening the dominant population is an important means to improve the clinical benefit of patients and reduce clinical complications. With economic development the proportion of obese people in China and the world is increasing which has become a public health problem. There is growing evidence that obesity may affect the efficacy of immunotherapy and it has become an effective feature for screening immunotherapy -beneficial populations but the mechanism remains unclear. The 􀆵 obesity paradox refers to the fact that obesity leads to immunosuppression and promotes tumor progression in preclinical studies via chronic inflammation the creation of an immunosuppressive tumor microenvironment disturbance of adipokines secretion and reduction of beneficial bacteria in the gut microbiota but the clinical studies show that obese people can benefit more from immunotherapy. In order to provide research directions and theoretical basis to explore the real impact of obesity status on the efficacy of immunotherapy in the future and to improve the efficacy of immunotherapy we reviewed the impact of obesity on the efficacy of immunotherapy from both clinical and preclinical studies and proposed possible explanations for the 􀆵obesity paradox .