Background: Ascites refers to the accumulation of fluids in the abdomen, leading to abdominal enlargement and complications of the peritoneal cavity.Objectives: This study aimed to evaluate the diagnostic efficacy of ultrasonography in identifying the causes of ascites in hybrid dog breeds.Methods: The current retrospective cross-sectional study involved 21 dogs of hybrid breeds (12 males and 9 females) with an Mean±SD age of 6.70±0.49 years and a Mean±SD weight of 24.37±3.65 kg. In a radiology ward, a radiologist examined the dogs by conducting an abdominal cavity ultrasound to diagnose and report the cause of ascites. Notably, the radiologist knew nothing about the history, clinical symptoms, and laboratory findings regarding the dogs. After the definitive cause of ascites was determined, the result was compared with the ultrasonographic diagnosis, calculating its sensitivity, specificity, and accuracy.Results: Liver diseases, renal conditions, and malignancies were identified as the most common causes of ascites. Based on the results, ultrasonographic diagnosis revealed the following specifications: 97.8% specificity, 91.1% sensitivity, 94.4% accuracy, 97.8% positive predictive value, and 91.1% negative predictive value.Conclusion: In general, the research results indicate that ultrasonography can serve as a primary tool for diagnosing the early stages of ascites. In a few cases where diagnosis of the underlying cause proves challenging, this method helps reach a subsequent diagnosis, except in cases involving liver and renal complications. Also, ultrasonographic diagnosis gets around invasive techniques such as sampling and laparoscopy, reducing the hospitalization period, hospital costs, and patient stress and also facilitating the medical process.