MicroRNAs (miRNAs) are non-coding regulatory RNAs consisting of 20-24 nucleotides. Over 4,500 miRNAs have been identified in humans, and it is known that nearly all human protein-encoding genes can be controlled by miRNAs in both healthy and malignant cells. Abnormal miRNA expression is known to occur in many cancers, including in malignant lymphomas (MLs). Detailed genome-wide miRNA expression analysis has been performed in various ML subtypes, and these analyses have led to the discovery of subtype-specific miRNA alterations. Actually, in B-cell lymphomas, several miRNAs have been used as prognostic markers, and their targets are for new agents for ML therapy. Successful studies for delineating miRNA functions in B-cell lymphomas lead us to hypothesize that miRNA dysregulation may also be deeply associated with the pathogenesis of T-cell lymphomas. Indeed, studies for delineating essential miRNAs have been conduced against comparatively well-defined T-cell lymphoma entities. In this review, we describe several key miRNAs and their targets in distinct T-cell lymphoma subsets and their roles in their pathogenesis, studies of which will lead to new therapeutic strategies against T-cell lymphomas.