Abstract: Marine nanoplanktonic diatoms have been frequently either underestimated or overlooked in phytoplankton investigations due to their small size (2-20 m) which will mostly pass through a regular phytoplankton net of 76 m pore size. For nanoplanktonic diatom classification, water samples (each 2000 mL) were collected from several representative sea areas of China coast. Nanofrustulum Round, Hallsteinsen & Paasche was identified as a newly recorded diatom genus for China under transmission electron microscope (TEM). Its sole species was found, i.e., N. shiloi (Lee, Reimer & McEnery) Round, Hallsteinsen & Paasche. Detailed description of the taxonomic characteristics with TEM photographs of this species and its ecological behavior and distribution are given in this paper. Morphological characteristics comparisons among several resembling genera were discussed.