Introduction: Interleukin (IL)-34, a macrophage (Mø) mediator, is expressed by tubular epithelial cells. However, the influence of IL-34 on tubulointerstitial fibrosis remains to be fully elucidated. We investigated the effect of IL-34 on renal fibrosis caused by unilateral ureteral obstruction (UUO). Material and Methods: 10-week-old male C57BL/6 (B6) mice (n=16) were induced UUO. Groups of animals were given either anti-mouse IL-34 antibody (UUO+anti-IL-34 Ab, 400 ng/kg, n=8) or vehicle (UUO+V, equal volume of saline, n=8) daily by intraperitoneal injection. Four age-matched male B6 mice received sham operation as control. All mice were sacrificed on day 10. Results: Compared to the control, the UUO+V mice exhibited remarkable intrarenal expressions of IL-34 and its two receptors (cFMS and PTP-ζ), which were significantly suppressed by anti-IL-34 Ab treatment. Compared to the UUO+V mice, tubular injury and sirius red positive area were significantly attenuated in the UUO+anti-IL-34 Ab mice. Treatment with anti-IL-34 Ab significantly suppressed the number of F4/80⁺ Mø and α-SMA⁺ myofibroblast in damaged kidneys of UUO. The renal cortical transcript levels of TGF-β, COL-1, TNF-α, IL-6, MCP-1/CCL2, and MIP-1/CCL3 were significantly lower in the UUO+anti-IL-34 Ab mice. Conclusion: Elevated IL-34 expression was related to renal fibrosis. Inhibition of IL-34 with neutralizing Ab suppressed expressions of inflammatory cytokines and fibrogenetic genes via reducing the Mø infiltration, which might lead to attenuate the development of renal fibrosis.