microRNA (miRNAs) is a newly identified class of 20-24 nt non-protein-coding and endogenous small RNA, which plays an important role in plant growth, development and response to environmental stresses. Combined with bioinformatic method, the types, abundance, and targets of known miRNAs in root and leaf of maize (Zea mays L.) were analyzed by small RNA deep sequencing technology, which was based on Illumina/Solexa principium. The results indicated that 92 known miRNAs were detected in maize root, which were attributed to 18 miRNA families and their abundance ranged from 1 to 105,943 reads. Synchronously, 86 known miRNAs were detected in maize leaf, which were attributed to 17 miRNA families and their abundance ranged from 1 to 85,973 reads. The target gene prediction showed that 54 putative target genes as these known miRNAs were predicted. Some of them were involved in the following processes, such as transcription regulation, substance and energy metabolism, electron transport, stress response, and signal transduction through further function prediction. In conclusion, there were obvious differences in both types and abundance of known miRNAs between root and leaf in maize.