Purpose: In order to clarify the optimal timing for peripheral blood stem cell ( PBSC) collection, PBSC collection records of 323 children who were scheduled to undergo autologous stem cell transplantation from two study periods differing in the timing of PBSC collection were analyzed. Methods: In the early study period (March 1998 to August 2007, n = 198), PBSC collection was initiated when the peripheral WBC count exceeded 1,000/μL during recovery from chemotherapy. Findings in this study period indicated that initiation of PBSC collection at a higher WBC count might result in a greater CD34sup＞+/sup＞ cell yield. Therefore, during the late study period (September 2007 to December 2012, n = 125), PBSC collection was initiated when the WBC count exceeded 4,000/μL. Results: Results in the late study period validated our conclusion from the early study period. Collection of a higher number of CD34sup＞+/sup＞ cells was associated with a faster hematologic recovery after transplant in the late study period. Initiation of PBSC collection at WBC count ＞ 4,000/μL was an independent factor for a greater CD34sup＞+/sup＞ cell yield. Conclusion: PBSC collection at a higher WBC count is associated with a greater CD34sup＞+/sup＞ cell yield, and consequently a faster hematologic recovery after transplant.