To investigate the effect of phenolics in mulberry leaves (mulberry leaf phenolics; MLP) on hyperglycemia-induced oxidative stress and mitochondrial membrane potential (ΔΨm) in HepG2 cells; we treated HepG2 with glucose [5.5 (N-Glc) or 50 mmol/L (Hi-Glc)] with or without MLP at 10 or 100 µmol/L gallic acid equivalents and assessed level of reactive oxidant species (ROS), ΔΨm, malondialdehyde (MDA) and nuclear factor-kappaB (NF-κB) activation. Hi-Glc-induced oxidative damage was demonstrated by a series of increase in superoxides (560%, 0.5 h), MDA (400%, 24 h), NF-κB activation (474%, 4 h) and a wild fluctuation of ΔΨm relative to the control cells (p ≤ 0.05). MLP treatments ameliorate Hi-Glc-induced negative effects by a 40% reduction in ROS production, 34-44% reduction in MDA production, over 35% inhibition of NF-κB activation, as well as exert protective effect on HepG2 cells from change in ΔΨm. Our data show that MLP in vitro can protect hepatoctyes from hyperglycemia-induced oxidative damages.