MicroRNAs (miRNAs) are a family of 21-25 nucleotide small nonprotein-coding RNAs. They regulate gene expression at post-transcriptional level by mRNA degradation or translation repression. Hematopoiesis is one of the most important highly regulated multistage process, which includes orderly turn-on and turn-off of many genes; any wrong modulation may result in blood diseases. Several miRNAs have been found to be involved in hematopoiesis and hematopoietic tumor genesis.