Pneumonia is one of the most common complications for patients with stroke. Recently, more and more attention has been paid on the roles of immune system in pneumonia and immunosuppression after stroke has been regarded as an independent risk factor for infections. Experimental and clinical studies have identified a series of inflammation and immunosuppression after stroke, including the reduction of mononuclear phagocyte and natural killer cell function, induction of anti-inflammatory cytokines, apoptosis of lymphocyte and alteration of T lymphocyte activity. The mechanism is likely to be that immunosuppressive signals impact on the nervous system through the hypothalamus-pituitary-adrenal axis, sympathetic adrenergic axis, and the parasympathetic adrenergic axis, which lead to the changes of immune system and down-regulation of immune function as well. In addition, some other studies attested that stroke-induced immunosuppression had protective effect on the brain. The mechanism regarding immunosuppression remains unclear now but do exist. Obviously, the further research on the stroke-induced immunosuppression will have great significance on the prevention of pneumonia after stroke.