Treatment of acute postrenal ureteral obstruction is a rather complicated, but extremely necessary process. It includes both surgical techniques to resolve the obstruction, and drug treatment, which largely affects the patient’s recovery period. The main goal in the postoperative period is to reduce the indicators of azotemia in these patients. Its main aspects are liquid therapy, antibiotic therapy and alpha 1‑adrenoblockers to relax the smooth muscle of the urethra. The objective of the research was to study how the replacement of ¼ of the total volume of crystalloid solutions in liquid therapy, calculated according to the formula of deficient and supportive volume, with colloidal solutions and blood plasma affects the restoration of blood parameters in the postoperative period; how an increase in the volume of oncotic pressure affects the effectiveness of reducing azotemia in patients in the postoperative period. 3 groups of 3 patients with createnine values in the range of 700–1000 mmol/L were selected. All underwent surgery in the form of ureteral reimplantation, which resolved the cause of the obstruction. Further, blood counts were monitored on DRI-CHEM NX500 analyzers and the Heska Element HT5 general clinical analyzer for 14 days after surgery and on 3,5,7,14 days from the date of observation. All groups showed a decrease in azotemia. However, there were differences in the effectiveness of the reduction. Patients receiving a crystalloid solution showed the most effective reduction of azotemia, unlike patients receiving liquid therapy, which includes protein inclusions. However, liquid therapy with blood plasma in the protocol showed a slightly better decrease than with colloidal solution. We conclude that drugs containing protein inclusions are not the drugs of choice in the case of correction of the condition in cats with benign unilateral ureteral obstruction.