It is known that respiratory syncytial virus (RSV) is the main cause of bronchiolitis and pneumonia in young children. RSV infection often leads to severe acute lung immunopathology, but the underlying immune mechanisms are not yet fully elucidated. Here, we found that RSV infection induced severe acute lung immune injury and promoted the accumulation and activation of lung natural killer (NK) cells at the early stage of infection in BALB/c mice. Activated lung NK cells highly expressed activating receptors NKG2D and CD27 and became functional NK cells by producing a large amount of gamma interferon (IFN-γ), which was responsible for acute lung immune injury. NK cell depletion significantly attenuated lung immune injury and reduced infiltration of total inflammatory cells and production of IFN-γ in bronchoalveolar lavage fluid (BALF). These data show that NK cells are involved in exacerbating the lung immune injury at the early stage of RSV infection via IFN-γ secretion.