This randomized, open-label, multicenter phase II study is designed to compare disitamab vedotin plus radiotherapy with gemcitabine plus carboplatin as adjuvant treatment in patients with HER2-expressing upper tract urothelial carcinoma after radical nephroureterectomy (RNU). Eligible patients must have postoperative pathologic stage pT3-pT4N0M0 or pTanyN+M0, HER2 expression defined as immunohistochemistry (IHC) 1+, 2+, or 3+, and be cisplatin-ineligible. Patients will be randomized in a 2:1 ratio to receive disitamab vedotin plus radiotherapy or gemcitabine plus carboplatin. The primary endpoint is 3-year disease-free survival. Secondary endpoints include overall survival, metastasis-free survival, local recurrence-free survival, bladder recurrence-free survival, incidence of adverse events, and patient-reported quality of life.