The article presents the results of research on the experience of using drug Mirtazapine in combination therapy of idiopathic cystitis in cats. It has been found that the use of Mirtazapine for cats with idiopathic cystitis at the dosage of 1.88 mg per day for two weeks improves the overall state and cognitive functions. The drug has a pronounced analgesic effect. Mirtazapine does not cause changes in the hematological parameters of cats. In addition, injection of Mirtazapine reduces the pH value of urine after 14 days by 6.7 %, after 30 days — by 10.7 %, and after 60 days — by 10.3 %, compared to the first day. A decrease of 3.5 % (30 days) and 7.6% (60 days) of pH was also noted in animals in the second group. All of these allow concluding the reasonability of using Mirtazapine for cats with idiopathic cystitis.