A 4-year-old child with β-thalassemia major underwent allogeneic hematopoietic stem cell transplantation (HSCT) on August 30, 2022 from a male haploidentical donor. He developed massive pericardial effusion (PE) secondary to a pulmonary infection. Methylprednisolone, tacrolimus discontinued, and pericardiocentesis were all ineffective. Since the interleukin-6 (IL-6) level in the PE was markedly increased (1868.58pg/ml), a total of two doses of tocilizumab was administered intravenously at a dosage of 5mg/kg every 2 weeks. PE remarkably reduced and completely resolved within 8 days. No recurrence of PE was observed in the follow up visits. Our results suggest that tocilizumab can be considered as a treatment of choice in massive PE after HSCT.