Objective To compare the immune response of specific CD8⁺ T cells induced by H1N1 Influenza A virus PR8 strain in the lungs of young and aged C57BL/ 6 mice. Methods Young ( 3 months) and aged ( 24 months) mice were intranasally infected with 490 plaque-forming units of PR8, then 8 days later, they were euthanized and their lungs collected. Fluorescence-activated cell sorting was used to compare the number and functions of viral antigen-specific CD8⁺T cells between the young and aged mice. Surface staining for the influenza virus MHC-I tetramer was performed to count the antigen-specific CD8⁺T cells; and intracellular cytokine staining was used to quantify the cytokines secreted by CD8⁺ T cells in response to influenza-specific peptides, including tumor necrosis factor ( TNF-α ), interferon-γ, interleukin-2, and granzyme B, which are involved in killing by CD8⁺ T cells.Results The proportion of virus-specific CD8⁺T cells in the aged mice was significantly lower than in the young mice. Moreover, the expression of interferon-γ, TNF-α, and interleukin-2 in activated CD8⁺T cells from the aged mice was significantly lower than in the young mice. In addition, the level of granzyme B expression on CD8⁺T cells in the aged mice was significantly lower. Conclusions The number of specific CD8⁺T cells induced by PR8 influenza virus was lower, and their function was impaired in the lungs of aged C57BL/ 6 mice compared with young mice. This implies that the response by specific CD8⁺T cells in the lungs of mice is impaired by aging.