Activation of the polyol pathway has been linked to the development of secondary diabetic complications. However, the underlying molecular mechanisms remain unclear. To probe the contribution of this pathway, we examined whether inhibition of aldose reductase, which catalyzes the first step of the pathway, affects hyperglycemia-induced activation of the inflammatory transcription factor nuclear factor (NF)-κB. Treatment of vascular smooth muscle cells with the aldose reductase inhibitors tolrestat and sorbinil prevented high-glucose–induced protein kinase C (PKC) activation, nuclear translocation of NF-κB, phosphorylation of IKK, and the increase in the expression of intracellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, and aldose reductase. High-glucose–induced NF-κB activation was also prevented by the PKC inhibitors chelerythrine and calphostin C. Ablation of aldose reductase by small interference RNA (siRNA) prevented high-glucose–induced NF-κB and AP-1 activation but did not affect the activity of SP-1 or OCT-1. Stimulation with iso-osmotic mannitol activated NF-κB and increased the expression of aldose reductase but not ICAM-1 and VCAM-1. Treatment with aldose reductase inhibitors or aldose reductase siRNA did not affect mannitol-induced NF-κB or AP-1 activation. Administration of tolrestat (15 mg · kg⁻¹ · day⁻¹) decreased the abundance of activated NF-κB in balloon-injured carotid arteries of diabetic rats. Collectively, these results suggest that inhibition of aldose reductase, which prevents PKC-dependent nonosmotic NF-κB activation, may be a useful approach for treating vascular inflammation caused by diabetes.