In the course of our studies on the constituents of the zoanthid Palythoa tuberculosa, we have isolated some water soluble compounds with a strong absorption maximum at 310-360 nm, and have already reported the structure of two of these compounds, mycosporine-Gly (λmax 310 nm) and palythine (λmax 320 nm). On the other hand, it is well known that compounds with an absorption maximum at 310-340 nm are present in many marine plants and animals, however there are few reports on the structure and the role in vivo. Recently, Tsujino et al. have isolated a compound with an absorption maximum at 320 nm from red alga Chondrus yendoii, which has the same structure as palythine from Palythoa tuberculosa. By further investigations on the UV absorbing compounds from Palythoa tuberculosa, two new compounds with an absorption maximum at 332 and 360 nm have now been assigned structures 3 and 4 and named palythinol and palythene, respectively. An oily material containing palythinol was obtained by repeated chromatography of aqueous EtOH extracts of Palythoa tuberculosa on TSK G-3000s (polystyrene gel; eluent: H2O) and Dowex 50N (H+ form; eluent: 0.5N HCl), then purification by preparative TLC on silica gel gave palythinol as yellow crystals. Palythene was eluted from TSK G-3000s with 10% aqueous EtOH after eluting mycosporine-Gly, palythine and palythinol with water, then purification by preparative TLC on silica gel provided palythene as yellow crystals. Through spectral data (UV, PMR, CMR, IR, MS) and chemical reactions (e.g., treatment of palythinol with diazomethane in ether-MeOH to form a methyl ester, treatment with concentrated NH4OH at room temperature overnight to afford compound 1, 2-aminopropanol and glycine; hydrogenation of palythene with Pd-C as a catalyst in H2O for 1 hr to afford dihydro-palythene), the planar structures of palythinol and palythene were established. The stereochemistry of the amino propene moiety of palythene was determined by PMR measurements, where the coupling constant of two olefinic protons (13 Hz) clearly indicated a trans-relationship. Thus, four UV absorbing amino acids, mycosporine-Gly, palythine, palythinol and palythene, have been isolated from Palythoa tuberculosa and the planar structure of these compounds has been determined. These compounds are characterized by the presence of a cyclohexene ring and a glycine moiety. As a series of these compounds is widely present in many marine plants and animals, the role and the biogenesis of these compounds in vivo are very interesting.