Abstract: The absorption spectra of 10 species of marine algae, including 4 species of green algae, 3 species of brown algae and 3 species of red algae, collected from Tsingtao were measured by Shibata's opal glass method. The characteristics of the absorption spectra of these three groups of algae, the absorption maxima and bands of chlorophylls, phycobilins and fucoxanthin in vivo were discussed on the basis of the absorption spectra of these marine algae and the difference spectra between the brown or red algae and the green algae. The results were presented in Table 1. On the basis of the results from the comparative studies on the differences between the absorption spectra of brown algae and those of green algae and on the difference spectra of green algae at 485 (or 480) μm were attributed to blue band absorption maximum of chlorophyll b, thus supporting the view point of Barer (1955) and French (1960). In the difference spectra between brown and green algae, the negative peak at 655 μm and the peak at 525 μm show repectively the positions of the absorption maximum of the red band of chlorophyll b in green algae and of fucoxan-thin in brown algae. On the basis of the absorption spectra of red algae and the characteristics of the red band absorption peak and the negetive peak in the difference spectra between red and green algae, the red band absorption peak of the chlorophyll d of red algae in vivo appeared to be located at a longer wave position than that of the red band absorption peak of chlorophyll a. Comparative studies of the absorption spectra of three species belonging to two different classes of red algae, namely, Porphyra yezoensis of the more primitive class Bangiophyceae or Protoflorideae, and Halymenia sinensis and Phycodrys radicosa of the more advanced Floridophyceae, showed marked differences in these two groups of red algae. Members of the Floridophyceae including the Halymenia, the Phycodrys and four other species, all showed three phycoerythrin absorption peaks, respectively at 500, 540 (or 535) and 560 μm, differening from each other only slightly in heights, as previously reported for other Floridophyceae by Haxo and Blinks (1950) and Saenger et al (1969). Whereas in Porphyra of the Bangiophyceae, there were only two absorption peaks, respectively at 500 and 565 μm, differening significantly from each other in height. As we have previously reported, marked differences in the amount and composition of their phycobilin contents were shown between Porphyra yezoensis from regions with rich mineral nutrients and those from regions with meagre mineral nutrients, as well as between the different portion of the same thallus. It is therefore suggested that presence of such variations and differences of the phycobilin systems in the red algae may be of significance in the study of the evolution of this group of algae and in the study of ecological adaptation.