This study was aimed to investigate the influence of timing using G-CSF after chemotherapy on graft yield of mobilized peripheral blood stem cells for autoPBSCT. 39 patients with lymphoma or multiple myeloma (MM) received the same chemotherapy mobilization regimen, including CTX 400 mg/m² d1; VLB 2 mg/m(2) d1; Ara-C 60 mg/m ²× d1-5; VP-16 60 mg/m² × d1-5; and prednisone 40 mg/m² × d1-5. The historical control group (12 cases) received G-CSF subcutaneously (filgrastim) at the first restoration after the initial nadir of the peripheral WBC count. The experimental group (27 cases) received G-CSF during the steady rise of the WBC count (end of fluctuating after initial nadir). G-CSF was given in a single daily subcutaneous dose of 5 µg/kg until the final PBSC apheresis. When the peripheral WBC and mononuclear cell (MNC) counts reached 10 × 10⁹/L and 1.0 × 10⁹/L respectively, leukapheresis was carried out using the COBE Spectra blood cell separator. The results indicated that despite there was comparable treatment with alkylating agents between 2 groups, a significantly increased yield of CD34 positive cells was observed in the experimental group (26.4 × 10⁶/kg), as compared to the historical control group (3.1 × 10⁶/kg) (p = 0.0031). It is concluded that the appropriate timing for the use G-CSF mobilization after chemotherapy is important to increase the CD34(+) cell yield in auto-graft.