Two cases of eosinophilic cystitis are reported. Case 1 was a 7-year-old boy with pollakisuria and case 2 was a 20-year-old man with right lower abdominal pain. They were suspected of bladder sarcoma after the examinations by cystoscopy, IVP, ultrasonography, CT and NMR-CT. Transurethral, percutaneous and open biopsies were performed and histological examination revealed massive infiltration of eosinophils mainly in the vesical muscle layer without malignant cells. We could establish the diagnosis only by biopsy. In case 1, IgE RAST was positive for tick and case 2 seemed to be allergic to rare beef. We presumed that they caused eosinophilic cystitis.