Vascular calcification (VC) is a major cause of mortality in patients with end-stage renal diseases. Biomarkers to predict the progression of VC early are in urgent demand. We identified circulating, cell-free microRNAs as potential biomarkers using in vitro VC models in which both rat and human aortic vascular smooth muscle cells were treated with high levels of phosphate to mimic uremic hyperphosphatemia. Using an Affymetrix microRNA array, we found that miR-125b and miR-382 expression levels declined significantly as biomineralization progressed, but this decline was only observed for miR-125b in the culture medium. A time-dependent decrease in aortic tissue and serum miR-125b levels was also found in both ex vivo and in vivo renal failure models. We examined the levels of circulating, cell-free miR-125b in sera from patients with end-stage renal diseases (n=88) and found an inverse association between the severity of VC and the circulating miR-125b level, irrespective of age or mineral-related hormones (odds ratio, 0.71; =0.03). Furthermore, serum miR-125b levels on enrollment can predict VC progression years later (for high versus low, odds ratio, 0.14; <0.01; for the highest versus lowest tertile and middle versus lowest tertile, odds ratio, 0.55 and 0.13; =0.3 and <0.01, respectively). The uremic VC prediction efficacy using circulating miR-125b levels was also observed in an independent cohort (n=135). The results suggest that serum miR-125b levels are associated with VC severity and serve as a novel predictive marker for the risk of uremia-associated calcification progression.