Gracilaria verrucosais a red alga that is widely distributed in seaside areas of many countries. We examined the effect ofG. verrucosaextract on adipogenesis, reactive oxygen species (ROS) production, and glucose uptake in 3T3-L1 cells. Oil red O staining and a nitroblue tetrazolium assay showed thatG. verrucosaextract inhibited lipid accumulation and ROS production, respectively. mRNA levels of adipogenic transcription factors, peroxisome proliferator-activated receptor gamma and CCAAT/enhancer-binding protein alpha, as well as of their target gene, adipocyte protein 2, were reduced upon treatment withG. verrucosaextract. However,G. verrucosaextract increased glucose uptake, glucose transporter-4 expression, and AMP-activated protein kinaseα (AMPKα) phosphorylation compared to the control. Our results suggest that the anti-adipogenic and insulin-sensitive effects ofG. verrucosaextract can be recapitulated to activation of AMPKα. Copyright © 2012 John Wiley & Sons, Ltd.