<p>Microalgae attract significant attention as promising biofuel sources. However, lack of an efficient genetic transformation system hinders their use in advanced genetic engineering applications. We previously identified the marine oleaginous microalgal strain, NKG400014, from our marine microalgal culture collection via Nile red screening. Subsequent phylogenetic analysis revealed that strain NKG400014 belonged to the new genus, <i>Marinichlorella</i>. To date, successful genetic transformation of <i>Marinichlorella</i> species has not been reported. In this study, we aimed to investigate the growth characteristics of NKG400014 to clarify its oleaginous features as a biofuel producer. Then, we established a technique for NKG400014 genetic transformation via electroporation and optimized the key parameters. Two selectable markers (hygromycin phosphotransferase and neomycin phosphotransferase II genes) were used to assess the transformation efficiency under endogenous and exogenous promoters. Endogenous promoters of <i>Marinichlorella</i> sp. were more efficient for transformation than its exogenous promoters. To the best of our knowledge, this study represents the first successful genetic transformation of <i>Marinichlorella</i> sp.. Further development of genetic tools and metabolic engineering approaches can enhance the lipid productivity of this strain, facilitating the economic production of microalgal biofuels.</p>