OBJECTIVES: Maintenance avelumab therapy after first-line induction chemotherapy is a viable option in the evolving treatment paradigm for metastatic urothelial carcinoma (mUC); however, the clinical determinants of its efficacy remain unknown. Here, we explored the prognostic factors of maintenance avelumab therapy for mUC using a multicenter real-world database. METHODS: The review of the multicenter database identified 59 patients with mUC who did not progress during first-line chemotherapy and subsequently received maintenance avelumab therapy. Progression-free survival (PFS) and overall survival (OS) after the initiation of avelumab were analyzed, and prognostic factors were explored. RESULTS: The median age was 70 years, and the primary lesion was the bladder in 28 (47.5%) patients. In the first-line chemotherapy, gemcitabine plus cisplatin was administered in 40 (67.8%) patients. The number of chemotherapy cycles was 2-3/4/5/6 in 7 (11.9%)/22 (37.3%)/6 (10.2%)/24 (40.7%) patients. With a median follow-up period of 13.2 months, 38 (64.4%) patients progressed and 20 (33.9%) died. The median PFS and OS were 6.1 months and not reached, respectively. Multivariable analysis demonstrated that hypoalbuminemia was the only independent predictor of poor PFS (hazard ratio, 2.70; p = 0.013). Patients with hypoalbuminemia showed significantly shorter median PFS (3.3 vs. 12.0 months; p = 0.004) and OS (9.3 months vs. not reached; p < 0.001) compared to those with normal albumin. CONCLUSIONS: Hypoalbuminemia was an independent prognostic factor in patients with mUC who were treated with maintenance avelumab therapy. Efforts to preserve nutritional status and avoid hypoalbuminemia may help optimize its efficacy.