This study reports bioavailability and metabolism of fucoxanthin (FUCO) from brown algae Padina tetrastromatica in rats. Rats were divided into two groups (n = 25/group). Group one was fed basal diet (control) while the group two received retinol deficient diet (RD group) for 8 weeks. After confirmed RD in blood (0.53 micromol/l), rats were further sub-grouped (n = 5/sub group), intubated a dose of FUCO (0.83 micromol) and killed after 0, 2, 4, 6 and 8 h. The plasma levels (area under curve/8 h) of FUCO (fucoxanthinol (FUOH) + amarouciaxanthin (AAx)) was 2.93 (RD group) and 2.74 pmol/dl (control), respectively. No newly formed retinol was detected in RD rats intubated with FUCO. Besides FUOH (m/z 617 (M+H)(+)) and AAx (m/z 617 (M+H(-))(+)), other deacetylated, hydrolyzed and demethylated metabolites of bearing molecular mass at m/z 600.6 (FUOH-H(2)O), m/z 597 (AAx-H(2)O), m/z 579 (AAx-2H(2)O+1), m/z 551 (AAx-2H(2)O-2CH(3)+2) and m/z 523 (AAx-2H(2)O-4CH(3)+4) were also detected in plasma and liver by LC-MS (APCI). Although biological functions of FUCO metabolites need thorough investigation, this is the first detailed report on FUCO metabolites in rats.