Micro RNAs (miRNAs) play an important role during renal development and show a tissue-specific enrichment in the kidney. Nephroblastomas, embryonal renal neoplasms of childhood, are considered to develop from nephrogenic rests (NRs) and resemble morphologically and genetically developing kidney. We therefore investigated the role of kidney-enriched miRNAs in the pathogenesis of nephroblastomas. miR-192, miR-215 and miR-194 had a significantly lower expression in nephroblastomas regardless of the subtype compared with mature kidney measured by quantitative real-time-PCR. miR-141 and miR-200c showed a significantly lower expression in blastema-type and mixed-type tumors. In comparison with NRs, a significantly lower expression of miR-192, miR-194 and miR-215 was identified in blastema-type, mixed-type and stroma-type nephroblastomas and of miR-141 and miR-200c in blastema-type tumors. Kidney parenchyma had a significantly higher expression of miR-192, miR-194, miR-215 and miR-200c compared with NRs. In this study, the activin receptor type 2B (ACVR2B), a member of the transforming growth factor (TGF)-β pathway, was identified as single common target gene for miR-192, miR-215, miR-194, miR-141 and miR-200c in silico for the first time. The interaction between all five miRNAs and ACVR2B was also verified by an in vitro assay. Additionally, a distinct protein expression of ACVR2B was detected in 53 of 55 nephroblastomas paralleled by an upregulation of ACVR2B messenger RNA demonstrated in 25 nephroblastomas of all subtypes. A differential regulation of ACVR2B by miRNAs in NRs and nephroblastomas appears to be an important step in the pathogenesis of nephroblastomas implicating for the first time the TGF-β pathway in this process.