The management of severe late-onset hemorrhagic cystitis (LO-HC) after allogeneic hematopoietic stem cell transplantation (HSCT) is still challenging. Because mesenchymal stromal cells (MSCs) possess anti-inflammatory and tissue repair-promoting properties, we retrospectively analyzed the efficacy and safety of MSC infusions in 7 of 33 patients with severe LO-HC after allogeneic HSCT. During treatment, each patient received at least one MSC infusion of Wharton's jelly derived from the umbilical cord of a third-party donor. In 6 patients, MSC treatment was initiated within 3 days of gross hematuria onset, while the 7th patient received an infusion 40 days later. The median dose was 1.0 (0.8-1.6) × 106/kg. Five of 7 patients responded to treatment. Notably, gross hematuria promptly disappeared in 3 patients after 1 infusion, with a time to remission not seen in patients without MSC infusion. Two patients showed no response even after several infusions. No acute or late complications were recorded. Our findings indicate that MSC transfusion might be a feasible and safe supplemental therapy for patients with severe LO-HC after allogeneic HSCT.