Objective: Kienböck disease is a rare condition characterized by severe pain and restricted wrist movement. Variouspalliative methods have been proposed as therapeutic strategies for alleviating symptoms. Mesenchymal stromal cell transplantationhas been suggested as an innovative and promising approach due to its potential for inducing regeneration andimmunomodulation in the necrotic tissue. This study aims to evaluate the safety of autologous bone marrow derivedmesenchymal stromal cells (BM-MSCs) transplantation after core decompression in Kienböck disease.Materials and Methods: In this phase I of an open-label clinical trial, three patients (one female and two males) withstage 2 Kienböck disease underwent autologous BM-MSCs transplantation following lunate core decompression. Thepatients were followed up for six months to assess safety as well as secondary clinical outcomes, including pain level,range of motion (ROM), and functional disability.Results: Safety of BM-MSCs injection following the core decompression was evaluated by recording post-treatmentcomplications during the six-month follow-up. No adverse events (AEs) or severe AEs (SAEs) were reported, indicatingthat BM-MSCs injection after core decompression is a safe intervention. All patients showed a remarkable reductionin visual analog scale (VAS) scores and "Disabilities of the Arm, Shoulder, and Hand" (DASH) questionnaire scores,suggesting the therapeutic potential of this intervention. Moreover, an increase in the ROM indicated that BM-MSCstransplantation can improve wrist functionality. Additionally, radiographic assessments before and after cell infusiondemonstrated a reduction in lunate sclerosis after six months of follow-up.Conclusion: The transplantation of autologous BM-MSCs following lunate core decompression seems to be a safeclinical intervention and may lead to pain relief in patients with Kienböck disease. Furthermore, this procedure may helpprevent disease progression during the follow-up period (registration number: NCT02646007).