Several researchers have proved that marine carotenoids have considerable potential and promising applications for human health. Among those carotenoids of marine origin, fucoxanthin (FX) acquired major part when compared to other marine carotenoids. FX has been reported to show numerous biological activities such as antioxidant, hepatoprotective, anti-inflammatory, anticancer, antidiabetic, antiobesity and neuroprotective effects. This chapter reviews the available scientific literature regarding the origin, metabolism, safety and biological activities of FX. It considers the conversion of FX into its metabolites and their characterization in different organs before the biological activity of FX can be understood. C. J. Rebello et al. showed the anti-obesity effects of FX and fucoxanthinol, where the carotenoids did not induce browning in human adipocytes. FX, a naturally occurring marine carotenoid, has shown biological activity against different human complication/disorders. The metabolites of fucoxanthinol were first isolated from sea squirt.