To investigate the effects of interaction between human bone marrow mesenchymal stem cells (MSCs) and K562 cells on the expression of proangiogenic factor IL-8, the K562 cells were co-cultured in direct contact with MSCs or cultured in MSCs conditioned medium while the controlled K562 cells were cultured alone. The IL-8 gene expression of K562 cells and MSCs was determined by RT-PCR. The results indicated that the expression of IL-8 in K562 cells when co-cultured in direct contact with MSCs or cultured in MSCs conditioned medium was obviously higher than that of K562 cells cultured alone (p<0.01). MSCs co-cultured with K562 cells also had an increased level of IL-8 compared with MSCs cultured alone (p<0.01). It is concluded that the interaction between MSCs and K562 cells via direct contact and the cytokine network promotes expression of IL-8.