Background: miRNAs are frequently dysregulated in the development of renal fibrosis. Exosomes are small membrane vesicles that could be isolated from urine secreted from all nephron segments. Here we sought to observe for the first time whether miRNA in urine exosome could serve as a potential biomarker of renal fibrosis. Methods: Urine samples were collected from 32 chronic kidney disease (CKD) patients who underwent kidney biopsy and 7 controls. Exosome was isolated and confirmed by immunogold staining of exosome marker. Members of miR-29, miR-200 and RNU6B as endogenous control were detected by RT quantitative PCR. Results: Electronic microscopy verified a typical shape of exosome with average size of 65.1nm and was labelled with anti-CD9 and anti-AQP2 antibody. Members of miR-29 and miR-200 are readily measured with reduced levels compared with controls (p<0.05), and can robustly distinguish CKD from controls (area under the curve (AUC) varied from 0.902 to 1 by ROC analysis).miR-29c correlated with both eGFR (r=0.362, p<0.05) and degree of tubulointerstitial fibrosis (r=-0.359, p<0.05) for CKD patients. Moreover, miRNAs in exosome was decreased in mild fibrosis group compared with moderated to severe group. miR-29a and miR-29c could predict degree of tubulointerstitial fibrosis with AUC of 0.883 and 0.738 (p<0.05). The sensitivity and specificity for distinguishing mild from moderate to severe fibrosis was 93.8%, 81.3% with the use of miR-29a, and 68.8%, 81.3% for miR-29c. Conclusions: Overall, miR-29c in urinary exosome correlates with both renal function and degree of histological fibrosis, suggesting it as novel, non-invasive marker for renal fibrosis.