Abstract: Objective To investigate the effect of microRNA on the gene expression profile of human leukemia K562 cells using microarray technique.Methods miR-181a RNA duplexes were designed and synthesized according to the mature sequence of miR-181a.Forty-eight hours after transfection of in vitro cultured K562 cells using OligofectamineTM,gene expression profiles of the cells were studied and analyzed using Agilent Human 1A Oligo microarray.Results Totalling 228 differentially expressed genes were identified from the 20 173 screened genes,including 59 up-regulated ones(consisting of metabolism-associated genes,tumor suppressor genes,signal transduction-associated genes,immunity and defense-associated genes etc),and 169 down-regulated ones(consisting of oncogenes,DNA-binding and transcription genes,metabolism-associated genes,signal transduction-associated genes,cell cycle and development-associated genes etc.)in the transfected K562 cells as compared with the control K562 cells.Changes in expressions of CTCF,ZAP70,SEMA4C and RALA were confirmed by semi-quantitative reverse transcription-polymerase chain reaction.Conclusions miR-181a transfection for 48 h induces gene expression profile changes in K562 cells,indicating the functionality of the miR-181a.These differentially expressed genes are related to the functions of the microRNA,and may also be the basis of the regulation model of posttranscriptional gene silencing.These findings provide an evidence for further study of the machineries and functions of the microRNA in mammalian cells.