Walnuts are a rich source of essential fatty acids, including the polyunsaturated fatty acids alpha-linolenic acid and linoleic acid. Essential fatty acids have been shown to modulate a number of cellular processes in the brain, including the activation state of microglia. Microglial activation can result in the generation of cytotoxic intermediates and is associated with a variety of age-related and neurodegenerative conditions. In vitro, microglial activation can be induced with the bacterial cell wall component lipopolysaccharide (LPS). In the present study, we generated a methanolic extract of English walnuts (Juglans regia) and examined the effects of walnut extract exposure on LPS-induced activation in BV-2 microglial cells. When cells were treated with walnut extract prior to LPS stimulation, production of nitric oxide and expression of inducible nitric oxide synthase were attenuated. Walnut extract also induced a decrease in tumor necrosis-alpha (TNFalpha) production. We further found that walnut extract induced internalization of the LPS receptor, toll-like receptor 4, and that the anti-inflammatory effects of walnut were dependent on functional activation of phospholipase D2. These studies represent the first to describe the anti-inflammatory effects of walnuts in microglia, which could lead to nutritional interventions in the prevention and treatment of neurodegeneration.