Diacylglycerol kinases (DGKs) convert diacylglycerol (DG) to phosphatidic acid, and both lipids are known to play important roles in lipid signal transduction. Thereby, DGKs are considered to be a one of the key players in lipid signaling, but its physiological function remains to be solved. In an effort to investigate one of nine subtypes, we found that DGK gamma came to be localized in the nucleus with time in all cell lines tested while seen only in the cytoplasm at the early stage of culture, indicating that DGK gamma is transported from the cytoplasm to the nucleus. The nuclear transportation of DGK gamma didn't necessarily need DGK activity, but its C1 domain was indispensable, suggesting that the C1 domain of DGK gamma acts as a nuclear transport signal. Furthermore, to address the function of DGK gamma in the nucleus, we produced stable cell lines of wild-type DGK gamma and mutants, including kinase negative, and investigated their cell size, growth rate, and cell cycle. The cells expressing the kinase-negative mutant of DGK gamma were larger in size and showed slower growth rate, and the S phase of the cells was extended. These findings implicate that nuclear DGK gamma regulates cell cycle.