Peroxisome proliferator-activated receptor-γ (PPARγ) are ligand-activated transcription factors that regulate cell growth, inflammation, lipid metabolism, and insulin sensitivity. We recently demonstrated that PPARγ agonists limit high glucose-induced inflammation in a model of proximal tubular cells (PTC; Panchapakesan U, Pollock CA, and Chen XM. Am J Physiol Renal Physiol 287: F528–F534, 2004). However, the role of PPARγ in the excess extracellular matrix production is largely unknown. We evaluated the effect of 24- to 48-h 8 μM l-805645 or 10 μM pioglitazone on 25 mM d-glucose-induced markers of fibrosis in HK-2 cells. High d-glucose induced nuclear binding of activator protein-1 (AP-1) to 140.8 ± 10.9% (P < 0.05), which was attenuated with L-805645 and pioglitazone to 82.3 ± 14.4 (P < 0.01 vs. high d-glucose) and 99.3 ± 12.2% (P < 0.05 vs. high d-glucose), respectively. High d-glucose increased total production of transforming growth factor (TGF)-β₁ 139.6 ± 6.5% (P < 0.05), which was reversed with L-805645 and pioglitazone to 68.73 ± 5.7 (P < 0.01 vs. high d-glucose) and 112 ± 13.6% (P < 0.05 vs. high d-glucose). L-805645 and pioglitazone reduced high d-glucose-induced fibronectin from 156.0 ± 24.9 (P < 0.05) to 81.9 ± 16.0 and 57.4 ± 12.7%, respectively (both P < 0.01 vs. high d-glucose). Collagen IV was not induced by high d-glucose. L-805645 and pioglitazone suppressed collagen IV to 68.0 ± 14.5 (P < 0.05) and 46.5 ± 11.6% (P < 0.01) vs. high d-glucose, respectively. High d-glucose increased the nuclear binding of NF-κB to 167 ± 22.4% (P < 0.05), which was not modified with PPARγ agonists. In conclusion, PPARγ agonists exert antifibrotic effects in human PTC in high glucose by attenuating the increase in AP-1, TGF-β₁, and the downstream production of the extracellular matrix protein fibronectin.