Acute kidney injury is a common problem in dogs and is associated with significant morbidity and mortality, so this study was aimed to evaluate Symmetric dimethylarginine (SDMA), Doppler ultrasonography including resistive index (RI) in the diagnosis of acute kidney injury in dogs. Ten healthy mongrel dogs were injected with gentamicin sulphate 10% at the dose of 30 mg/ kg body weight daily for ten days for induction of acute kidney injury. Clinical, Biochemical, Ultrasonographic, Doppler ultrasonographic examinations, and urinalysis were performed for all dogs on zero day before induction, on the 5th day, and the 10th day of induction. The results of the current study showed a significant increase in plasma level of SDMA, serum urea, creatinine, phosphorus, potassium, and a significant decrease in serum sodium, calcium, and chloride on the 5th day and 10th day of induction, there was an increase in renal cortical echogenicity of right and left kidney compared to adjacent liver and spleen, respectively. RI value showed a significant increase on the 5th day and 10th day of induction. This study showed that SDMA is a sensitive, and romising biomarker for diagnosis of acute kidney injury in dogs compared to routine biomarkers also, the RI of Doppler ultrasonography is useful for early identifying acute kidney injury when the only observable change is an increase in cortical echogenicity.