The purpose of the study is to study the pathomorphological picture of the urinary system in cats with triple phosphate urolithiasis. The study was carried out by using cadaveric materials from 18 cats diagnosed with triple phosphate urolithiasis on the basis of clinical signs (pollakiuria, hematuria, ischuria), and laboratory diagnostic methods (clinical studies of urine and blood, biochemical blood analysis). Macropreparations were studied visually by evaluating the linear size of the kidneys, condition of the capsule, surface appearance on the section, density, and the presence of inhomogeneous inclusions. The authors studied wall thickness of the bladder and urinary tract (urethra and ureters), their configuration, and condition of the mucous membrane on the section. Hematoxylin and eosin staining were used for histostructural diagnostics, as well as picrofuxin staining by Van Gison. During the study, it has been found that urolithiasis leads to structural changes in the urinary organs, while characteristics of organ and tissue damage vary depending on the duration of urolithiasis. The macroscopic study allows registering acute or chronic urocystitis, interstitial nephritis, sometimes with the deposition of concrements in the renal pelvis. The most significant microscopic changes are recorded in the renal tissues. Thus, renal changes are presented by conditions from acute interstitial nephritis to necrosis of renal tubules and nephrosclerosis. In the urinary tract (urethra and ureters) there are inflammatory changes with deposition of urolithes. These processes have seriously affect the general condition of animals and require quality control and the optimal selection of medicines during treatment. © 2018, Pharmainfo Publications. All rights reserved.