Introduction: Abundant myxoid stroma rarely occurs in urothelial carcinomas (UCs). We report an 83-year-old woman with UC of the urinary bladder with abundant myxoid stroma. We summarized the clinicopathological features, immunophenotype, diagnosis, and differential diagnosis of this type of bladder cancer, in order to improve the understanding of surgeons and pathologists. Patient concerns: An 83-year-old female presented with hematuria and frequent micturition, without odynuria, hypogastralgia, or fever. Diagnosis: The computed tomography scan demonstrated extensive tumors in the anterior wall of the bladder and a soft tissue shadow anterior to the sacrum. Cystoscopy showed massive wide-based tumors located on the anterior and lateral walls of the bladder, with no tumor involving the bladder neck. Multiple punch biopsies were performed, the histologic evaluation of which revealed a poorly differentiated invasive UCs with myxoid stroma. Interventions: The patient underwent a laparoscopic radical cystectomy and cutaneous ureterostomy. Outcomes: The patient discharged without any complications. Histologic evaluation revealed an invasive UC; the most prominent feature was an abundant myxoid stroma that covered approximately 80% of the lesion and the tumor cells were arranged in cords, small nests, or a sheet-like structure. Immunohistochemically, the tumor cells were positive for CK19, CK20, VEGF, EGFR, p63, 34 beta E12, MUC1, GATA3, uroplakin3, and TopII (rate = 15%), while the Ki-67 proliferation index was 10%. The myxoid stroma in the mesenchyme stained positively with AB-PAS and colloidal iron, and some tumor cells stained positive for colloidal iron. Considering the histologic, histochemical, and immunohistochemical findings, a diagnosis of UC with abundant myxoid stroma was made. After surgery, the regular follow-up was continued in clinic, and there was no recurrence for 2 years. Conclusion: Morbidity associated with UC with abundant myxoid stroma is very low. The diagnosis mainly depends on histopathological and immunohistochemical findings.