The extraction yield of fucoxanthin from Phaeodactylum tricornutum, a marine diatom, was investigated for 16h as the functions of the kind of solvent, temperature, and solvent/diatom weight ratio. Acetone, ethanol, and ethyl acetate were used as solvents for the extractions. The extraction yield increased in a saturation manner with the extraction time when the extraction temperatures were 30 degrees C and 40 degrees C. However, the extraction yield increased with time in the early stage of the extraction; thereafter, it was stagnant or decreased with time in the late stage at 50 degrees C, 75 degrees C, and 85 degrees C. The thermal deterioration would suppress the extraction yield in the late stage at those higher temperatures. The maximum extraction yield was obtained at 40 degrees C and no significant benefit in the extraction yield was obtained when the extraction period was extended over 12h. The extraction yield markedly increased when the solvent/diatom ratio increased from 3/1 to 6/1, but no marked benefit was obtained when the amount of solvent increased over the ratio of 6/1. Ethanol was the most effective solvent in the extraction of fucoxanthin, and the extraction yield was greater in the order of ethanol>acetone>ethyl acetate.