Background: Ehrlichiosis is a ricketsial disease transmitted by ticks and characterized by reticuloendothelial hyperplasia, fever, generalized lymphadenopathy, splenomegaly and thrombocytopenia. In this study, it was aimed to determine the blood vitamin D and D-dimer levels in dogs with Ehrlichiosis. Methods: The material of this study consisted of 33 dogs of different breeds, ages and both sexes during the period of 2018-2019. In 33 dogs with and without thrombocytopenia with clinical findings, definitive diagnosis and differential diagnosis were made with clinical examination and laboratory tests. All patients were evaluated for Ehrlichiosis with rapid Snap 4DX test kit. In addition, the diagnosis of the disease was made by PCR analysis. Blood D-Dimer levels were determined in control and study groups. Result: D-Dimer levels were significantly higher in the study groups when compared with the control group. Further, when blood D-vitamin levels of control and study groups were compared, it was found that blood D-vitamin levels were significantly lower in dogs with Ehrlichiosis. In conclusion, in this study, D-dimer levels were significantly increased in dogs with ehlichiosis and can be an adjunct biomarker with other clinical, hematologic and laboratory tests. In addition, serum vitamin D levels were found to be low in both active and acute infected patients in dogs previously exposed to the causative agent, which is closely related to the immune system of vitamin D and serum low vitamin D levels may pave the way for the development of ehrlichiosis disease.