Signal transducers and activators of transcription (STATs) are key DNA-binding proteins in JAK/STATs signal pathway. Aberrant expression and activation of STAT3 have been identified in many kinds of tumors. We report here that constitutive activation of STAT3 was present in BEL-7402 cells. We constructed the fusing genes of STAT3 (wild type/mutant) and GFP to study the function of constitutively activated STAT3 in BEL-7402 cells. By measuring the migration of the cells labeled by GFP-STAT3(WT/CYF), we proved that overexpression of STAT3(WT) could augment the migration of BEL-7402 cells, while STAT3(CYF) could decrease the migration.