Obesity and type II diabetes are rapidly taking a form of global epidemics. Fucoxanthin, a characteristic carotenoid found in brown seaweeds, has potential anti-obesity and anti-diabetic properties and may be effective for the treatment of these two conditions. The polyene chromophore tail of fucoxanthin, which contains an allenic bond and two hydroxyl groups, is believed to be a key factor for the bioactivities of the compound. Fucoxanthin induces mitochondria uncoupling protein 1 in white adipose tissue (WAT), which leads to increased heat production. In addition, fucoxanthin improves insulin resistance and decreases blood glucose levels through the regulation of cytokine secretion in WAT. This article provides a comprehensive review of the anti-obesity and anti-diabetes effects of fucoxanthin.