Eosinophilic cystitis is an uncommon disease which is characterized by eosinophilic infiltration into all layers of bladder. It was first described in 1959 by Brown and 50 cases have been reported in the literature. The presenting symptoms are frequency, urgency, dysuria and hematuria. It is chronic disease with remission and exacerbation and mimics other forms of chronic cystitis, such as interstitial cystitis, tuberculosis and bladder neoplasm. Diagnosis is made by biopsy. Treatment consists of removal of inciting allergens, corticosteroids, antihistamines, and antibiotics for secondary bacterial infection. Most women and children with eosinophilic cystitis had the history of allergic disease or asthma and most male patients had bladder or prostatic disorders, such as benign prostatic hypertrophy, bladder carcinoma, and congenital anomalies. But eosinophilic cystitis has not been found in diabetic patients yet. We report a case of eosinophilic cystitis in a 59- year-old diabetic patient with brief review of the literature.