This study was purposed to investigate the changes of bcl-6 expression in K562 cells and the mechanism inducing differentiation into different myelocyte lineages. Models of K562 cells inducing differentiation to lineages of megakaryocyte, erythrocyte and macrophagocyte were established with inducers TPA (tetradecanoylphorbol 13-acetate), Hu (hydroxyurea) and HMBA (hexamethylene bisacetamide) respectively. Western blot assay was applied to detect the expression of bcl-6 in K562 cells before and after the induction. Meanwhile, PCR, cloning and direct DNA sequencing were used to identify mutations in the 5' regulatory region of bcl-6 in K562 cells before and after induction with TPA. The results indicated that up-regulation of bcl-6 expression was found only in K562 cells being induced differentiating into megakaryocyte-lineage, while mutation of 5' regulatory region of bcl-6 gene was not found. It is concluded that expression of bcl-6 increases only when K562 cells differentiate into megakaryocyte lineage and bcl-6 expression may play an important role in K562 cells induced differentiation into megakaryocyte lineage. The up-regulation of bcl-6 expression may not be related with the mutation of 5' regulatory regions of the gene.