Plant and animal genomes contain an abundance of small genes that produce RNAs of about 22 nucleotides in length, which was dubbed as microRNA (miRNA). These newly found endogenous RNAs may participate in a wide range of genetic regulatory pathways and play an important role in the organism development. This paper reviewed the recent studies and progress on the characteristics, functions and mechanisms of the microRNAs, as well as the advances of research on lymphoid malignancies.