MicroRNAs (miRNAs) are a recently discovered class of post-transcriptional regulators that induce target messenger RNA degradation or translation inhibition. miRNA-155 (miR-155) is an important regulator of immune cells both in humans and mice, by which these cells play critical roles in the pathogenesis of rheumatoid arthritis (RA). Recent findings showed that expression of miR-155 was elevated in RA patients and arthritis models. Moreover, miR-155 overexpression or knockdown performed significantly in the development of arthritis. This review summarizes the recent findings with respect to miR-155 in immune responses and the underlying mechanisms responsible for miR-155-related autoimmune arthritis. Hopefully the information obtained will benefit the development of novel therapeutic strategies.