Three marine heterotrophic flagellates from intertidal sediments of Gwang-Am beach and Garorim Bay, Korea were identified as Neometanema parovale Lee and Patterson 2014, Stephanopogon pattersoni Lee et al. 2014 and Thaumatomastix sp. These species are reported taxonomically for the first time from Korea, and are described with illustrations and micrographs. Diagnostics of these species are as follows. Neometanema parovale (Euglenozoa): size in vivo, 10~23 μm long with 22 pellicular strips, ingestion apparatus barely visible by light microscopy and two flagella pointed in different directions when moving. Stephanopogon pattersoni (Percolozoa): size in vivo, 20~33 μm long, with 6 ventral and 1 ventro-lateral ciliary rows, and three barbs. Thaumatomastix sp. (Cercozoa): size in vivo, 14~17 μm with body scales and spines, and two flagella with one naked and one scaled.