A novel carotenoid ester, which had previously been assumed tentatively and without full supporting data to be loroxanthin 19-dodecenoate (Kohata and Watanabe 1989), was isolated and purified from cultured strains of Pyramimonas parkeae (Prasinophyceae) and a chlorarachniophycean alga. From spectroscopic and chemical evidence, including results of analysis by ¹H-NMR, FD-MS, GLC and CD, the compound was clearly identified as loroxanthin dodecenoate, (3R,3'R,6'R)-β,ε-carotene-3,19,3'-triol 19-(2-trans-dodecenoate). A double bond of the dodecenoate was located at the Δ² position and was in the trans form, as is the case for that in a siphonaxanthin ester. However, loroxanthin itself was absent from these algae. Other algal pigments identified were Chls a and b, β-carotene, lutein A, zeaxanthin, violaxanthin and neoxanthin.