Recently, peripheral blood stem cell (PBSC) has been widely used and replaced bone marrow (BM) as the stem cell source in allogeneic hematopoietic stem cell transplantation (HSCT) because of a more rapid engraftment, easier accessibility, and lower risk of donor complications. We, therefore, report the predicting factors for the high PBSC harvest yields in 50 healthy donors. Among the 50 donors, median collected CD34+ cell number was 4.6 × 106/kg (1.5–16.3 × 106/kg). Number of circulating CD34+ cells and hematocrit (HCT) level increased parallelly whereas peripheral CD34+ cell numbers were decreased with increasing donor age. In univariate analysis, HCT level≥ 35.5% at the time of PBSC collection was significantly associated with high PBSC number (≥ 5.0 × 106 cells/kg) and donor aged <30 years was significantly associated with collected CD34+ cells ≥ 6.0 × 106/kg, P = 0.03. HCT level ≥35.5% was an independent parameter for high WBC count (≥50 × 109/L), P < 0.05. None of donor who had both HCT < 35.5% and WBC < 50 × 109/L had circulating CD34+ cells ≥ 5.0 × 106/kg. Platelet count ≥ 200 × 109/L was found significantly in donors with WBC ≥ 40 × 109/L (P = 0.03) and HCT ≥ 35.5%, P < 0.05. Collected PBSC number tended to be higher in our donors with high levels of HCT, WBC, and platelet. We also found that HCT and platelet levels in our donors decreased after receiving G-CSF administration compared with the initial complete blood counts (CBC) results. We, therefore, concluded that HCT level at the time of initiation leukapheresis was an important predictor for PBSC collection yields. J. Clin. Apheresis 30:329–334, 2015. © 2015 Wiley Periodicals, Inc.