Objective To study the effect of granulocyte-macrophage colony-stimulating factor ( GM-CSF) secreting liver cancer vaccine on killing activity of cytotoxic T lymphocytes ( CTL) of transplanted liver cancer mice and its mechanism.Methods There were three groups:liver cancer vaccine group (A group), liver cancer group (B group) and PBS group (C group).The transplanted liver cancer model was builded with injection of H 22 hepatoma cells, while the GM-CSF secreting liver cancer vaccine group and PBS group was builded.GM-CSF secreting liver cancer vaccine group and PBS group were establised.The levels of CD8 +T cell in peripheral blood were detected by flow cytometry.The killing activity of cytotoxic T lymphocytes ( CTL) of spleen cells was detected by MTT method.The expression levels of tumor necrosis factor-α( TNF-α) and interferon-γ(γ-INF) were detected by Western blot.Results The flow cytometry results showed that, compared with B group, the levels of CD8 +T cell of A group significantly increased (P<0.01).MTT results showed that, compared with B group, the killing activity of cytotoxic T lymphocytes (CTL) in A group significantly increased (P<0.01).Western blot results showed that, compared with B group, the expression levels of tumor necrosis factor-α(TNF-α) and interferon-γ(γ-INF) in A group significantly decreased (P<0.01).Conclusion GM-CSF secreting liver cancer vaccine can significantly inhibit the activity of H22 cell, and its possible mechanism of action may be to activated CD8 +T expression, improve cytotoxic activity of CTL of spleen cells, and reduce TNF-αand γ-INF protein expression.