Previous studies highlight the need for a more active conditioning therapy in high-risk or refractory and relapsed lymphomas. Our preclinical research shows that histone deacetylase inhibitors, such as either vorinostat or chidamide, sensitize lymphoma cells to the cytotoxic combination of cladribine, gemcitabine and busulfan, leading to cell apoptosis. To evaluate the efficacy of this chidamide-cladribine-gemcitabine-busulfan (ChiCGB) combination as a new conditioning therapy, we conducted a Phase II trial, as described here. Patients with high-risk, relapsed/refractory lymphomas received ChiCGB as conditioning therapy, after transplantation with autologous peripheral stem cells. The sample comprised 105 patients in total: 60 with B-cell non-Hodgkin lymphomas (B-NHL) and 45 with T-cell or natural killer/T-cell lymphoma (NK/T). All patients eventually achieved full hematopoietic recovery. Neutrophils and platelets were engrafted at a median of 10 days (8-14) and 13 days (8-38), respectively. There was no transplant-related mortality within 100 days of transplant. Neutropenic fever, mucositis and atopic dermatitis were the observed nonhematologic toxicities. At a median follow-up of 35.4 months, 80.6% of the patients presented with no tumor progression, and the overall survival (OS) reached as high as 86.1%. Concerning the OS rate, 94.5% of patients with B-NHL and 75.4% of patients with T-cell or NK/T lymphomas survived. These findings demonstrate the safety and validity of the proposed combined therapy for high-risk and refractory/relapsed lymphomas. Our study was registered on the Clinical Trial Registry (clinicaltrials.gov, NCT03151876).© 2021 UICC.