Background and Aim: The present study investigated the influence of liver tumor structure on life expectancy in dogs. Diseases of the liver comprise 5-25% of all non-communicable diseases in dogs, and primary hepatic tumors account for 0.6-1.3% of tumors. This research aimed to study the post-operative life span of animals with primary or metastatic tumors of the liver. Materials and Methods: During the study period, 7124 oncological operations were performed in our clinic. In total, 128 liver tumors were detected in live animals, while 323 were detected posthumously. Forty animals underwent surgery for various liver tumors. In dogs with primary liver tumors, the average age was 11.9 years and the average body weight was 15.5 kg, while in dogs with liver metastases, the mean age was 11.4 years and the average body weight was 24 kg. Results: The ratio of males to females among dogs with primary liver tumors was about 1:1 (ten females and nine males), while that among dogs with metastatic liver damage was clearly predominantly female (14 females and two males) because females often undergo surgery for cancerous mammary glands or ovaries. Conclusion: The size of tumors and the number of affected lobes had a significant effect on the post-operative life span. With a tumor size of <5 cm and a lesion covering less than two lobes of the liver, life expectancy was significantly longer and the prognosis was more favorable. In cases of large tumors or those affecting more than two lobes, life expectancy was significantly reduced and the prognosis was cautious to unfavorable. Copyright: Vilkovyskiy, et al. © 2020 Veterinary World. All rights reserved.