Polyphenol-rich functional foods have shown promise in ameliorating NAFLD but the relative effectiveness and mechanisms of different polyphenols are largely unknown. In a model of steatosis using HepG2 hepatocytes exposed to palmitic acid, we investigated the effect of selected polyphenols (resveratrol, quercetin, catechin, cyanidin, kuromanin) and berberine. Exposure to palmitic acid produced steatosis and intracellular ROS production, which were prevented by all of the polyphenols and berberine, at 10 µM. Palmitic acid produced a 245% increase in mRNA for inducible nitric oxide synthase (iNOS) that was almost completely prevented by all of the polyphenols (but not by berberine). Most of the polyphenols also partially inhibited palmitic acid-induced increases in markers of endoplasmic reticulum stress, and decreases in mitochondrial content and mitochondrial membrane potential. In conclusion, the polyphenols all similarly prevented steatosis, ROS generation and iNOS induction, and protected against ER stress and mitochondrial impairment.