Brain can be roughly divided into two parts, cerebrum and cerebellum. Cerebrum controls higher brain functions including memory, emotion and cognition, while cerebellum is important for motor coordination. The only output neuron in cerebellum, Purkinje cell, regulates long term depression (LTD). LTD and morphology of Purkinje cells are important for motor function. So far, disorder of protein kinase C (PKC) α and γ, which are expressed in Purkinje cells, impaired LTD, morphology of Purkinje cells and motor coordination. Diacylglycerol kinase (DGK) γ phosphorylates diacylglycerol (DG) and is abundantly expressed in Purkinje cells. In other words, DGKγ can attenuate PKC activity by reducing amount of DG and may contribute to motor coordination. However, its physiological role has not been elucidated. Therefore, we developed DGKγ knockout (KO) mice and investigated their LTD, morphology of Purkinje cells, and cerebellar motor coordination. We found that cerebellar motor coordination and LTD were impaired in the DGKγ KO mice and the morphology of Purkinje cells from DGKγ KO mice was significantly retracted. Interestingly, abnormal activation of PKCγ was involved in impairment of the morphology of Purkinje cells from DGKγ KO mice. These results indicated that DGKγ was involved in cerebellar LTD and morphology of Purkinje cells, and DG signaling is important for cerebellar motor coordination.