During a survey of non-marine diatoms from the Marion Island, three new species, Pinnularia thoenii Van de Vijver sp. nov., Gomphonema marionense sp. nov. and Frustulia lebouvieri sp. nov. were recorded. The detailed morphologies of these three species are examined using both light (LM) and scanning electron (SEM) microscopy. Comparisons with similar species are discussed. Ecological information for each of the three species is given.