Latent signal transducers and activators of transcription(STATs) reside in the nucleus following cytokine stimulation and regulate gene expression upon activation of cytokine or growth factor receptors. While this translocation event is essential for gene regulation by STATs, their mechanism of transport through the cytoplasm to the nucleus has remained elusive. Nuclear shuttling molecules often own a mono or bipartite basic amino acid stretch, but STAT family do not own the classic nuclear localization sequence(NLS). Now, it is reported that STAT3 accumulate nucleus after IL-6 stimulation 20 min. With IL-6 stimulation, STAT3 molecule conformation changed and the NLS in DNA binding domain exposure to make it gain nuclear targeting function. Deleted a stretch(403～426aa) of basic amino acid in STAT3 DNA binding domain which destroys the nuclear importing function even with cytokine stimulation. It indicated that this stretch of basic amino acid has critical role for STAT3 nuclear import, which has nuclear localization sequence(NLS)function.