Differentiation of monocytes into dendritic cells (DCs) is characterised by marked changes in gene expression. The role of microRNAs (miRNAs), a new class of small endogenous non-coding regulatory RNAs, in this process is still unclear. We identified miR-223, miR-16, miR-191, miR-24, let-7b, and miR-21 as differentially expressed between monocytes and monocyte derived DCs. We evaluated the expression levels of computationally predicted target genes of miR-21 in human monocytes following stimulation with GM-CSF and IL-4. Moreover, transfection of monocytes with synthetic miR-21 inhibited the expression of a set of genes that were also repressed during monocyte differentiation to DCs in response to GM-CSF and IL-4. Among these, we identified genes that are involved in cell cycle, apoptosis and differentiation such as PDE4B, PDCD4, ANXA1, ING3, STAG2, TGFBI, S100A12, LAT2 and NRIP1. Collectively, the present study highlights the involvement of miRNAs, particularly miR-21 in monocyte differentiation to DCs and identifies potential miR-21 target genes.