SUMMARYCryotolerant eukaryotic microalgae were isolated from meltwater streams on Ardley Island and King George Island in Antarctica, and their morphological, molecular, and physiological characteristics were investigated. Owing to their simple morphology, distinctive characters were not observed with neither light microscopy nor transmission electron microscopy. However, molecular phylogenetic inferences drawn from the concatenated small subunit rRNA and internal transcribed spacer sequence data indicated that these microalgal strains belonged to the genus Micractinium. All the Micractinium strains showed cryotolerant properties, while their optimum growth temperature was around 20°C. Similar to other cryotolerant organisms, these Antarctic microalgae also contained a higher ratio of polyunsaturated fatty acids to saturated fatty acids. In this study, new Antarctic Micractinium spp. were discovered and added to the culture collection. These cryotolerant strains may serve as a promising source of nutritionally important linoleic (C18:2 ω6) and α-linolenic (C18:3 ω3) acids.