It has been proved that cyclooxygenase-2 (COX-2) is a key factor in lung cancer oncogenesis.COX-2 can be induced by a number of cytokines and growth factors and can be regulated by the JAK/STAT signaling pathway.Inhibiting the expression of COX-2 can prevent the development of lung cancer.The aim fo this study is to investigate whether the epidermal growth factor (EGF) can stimulate the signal transducers and activators of transcription 5 (STAT5) as well as to discover the effects of the STAT5 signaling pathway on the COX-2 in human lung adenocarcinoma A549 cells. The gene discussed is STAT5B; the disease is lung cancer.