The objective of this study was to assess the suppressive effects of 13 naturally occurring carotenoids on the adipocyte differentiation of 3T3-L1. The relationship between carotenoid structure and suppressive effects was also examined. Treatment with neoxanthin significantly reduced lipid accumulation, as well as glycerol-3-phosphate dehydrogenase activity. This suppressive effect on adipose cell differentiation was not observed in the other 12 carotenoids used in this study. Neoxanthin treatment also decreased expression of CCAAT/enhancer binding protein alpha (C/EBPalpha) and peroxisome proliferator-activated receptor gamma (PPARgamma) mRNAs. An examination of structure and function suggested that carotenoids containing an allene bond and an additional hydroxyl substituent on the side group may show suppressive effects on adipocyte differentiation in 3T3-L1 cells.