In this study, we reported a seldom case of pediatric high-grade B-cell lymphoma, not otherwise specified (HGBL, NOS) with loss of B-cell markers (CD19, CD20, CD22, CD79a, CD38, Pax5, OCT2, and BOB1) and CD45, which bring great challenges to exclude a non-lymphomatous neoplasm. However, no evidence was found to support the diagnosis of sarcoma and carcinoma. Thus, due to the patient’s prior history of Burkitt’s lymphoma treated by rituximab-containing therapies, we carefully searched for any indication of B-cell differentiation. Eventually, NGS results revealed the monoclonal rearrangement of IGH (IGHD2-8-IGHJ6 and IGHV4-30–2-IGHJ4) in both pre-treatment and present tumors, confirming the same B-cell lineage. Moreover, both tumors exhibited the same IGHA1-MYC translocation and somatic mutations of c-MYC, TP53, ID3, and CCND3. Therefore, in addition to strong expression of BCL2 in the present tumor, we finally arrived at a diagnosis of pediatric HGBL, NOS with loss of B-cell lineage markers and CD45.