This study was purposed to investigate the role of post-thaw infused donor cells for predicting engraftment and hematopoietic reconstitution after unrelated cord blood transplantation (UCBT). The retrospective analysis was performed on clinical data of 97 children with malignant or non-malignant diseases received single unit UCBT from August 1999 to April 2010. The impact of pre-freezing and post-thaw cell dose of total nucleated cells (TNC), CD34(+) cells and colony-forming units-granulocyte/macrophage (CFU-GM) on engraftment and hematological recovery after UCBT was analyzed. Unrelated donors were from Guangzhou cord blood bank (GZCBB) entirely. The results indicated that the pre-freezing TNC (/kg) (mean ± SD: 7.65 × 10⁷ ± 4.26 × 10⁷; median: 6.34 × 10⁷), CD34(+)cells (/kg) (mean ± SD: 4.64 × 10(5) ± 4.47 × 10⁵; median: 3.03 × 10⁵) and CFU-GM (/kg) (mean ± SD: 0.79 × 10⁵ ± 1.09 × 10⁵; median: 0.57 × 10⁵) showed a good correlation with their post-thaw counterparts including TNC(/kg) (mean ± SD: 6.98 × 10⁷ ± 4.12 × 10⁷; median: 6.00 × 10⁷), CD34(+)cells (/kg)(Mean ± SD: 6.86 × 10⁵ ± 8.56 × 10⁵; Median: 4.17 × 10⁵), and CFU-GM (/kg) (mean ± SD: 0.52 × 10⁵ ± 0.52 × 10⁵; median: 0.39 × 10⁵) (r = 0.952, p < 0.001; r = 0.794, p < 0.001; r = 0.478, p < 0.001). Either the pre-freezing or post-thaw number of infused CFU-GM was significant higher in patients who achieved engraftment (n = 70) than those who suffered graft failure (n = 22) (p = 0.023 and 0.011, respectively), but no significant difference of TNC and CD34(+) cells dose (pre-freezing or post-thaw) were found between these two groups. Pre-freezing CFU-GM, TNC, CD34(+) cell dose negatively correlated with the time of neutrophil engraftment (r = -0.285, p = 0.018; r = -0.396, p = 0.002; r = -0.373, p = 0.002), as well as the post-thaw number of TNC and CD34(+) cells (r = -0.260, p = 0.031; r = -0.483, p < 0.001), whereas only pre-freezing CD34(+) cells showed a significant correlation with platelet engraftment time (r = -0.352, p = 0.013). It is concluded that the CFU-GM amount is useful for predicting engraftment of UCBT, while pre-freezing hematopoietic cell doses show superior correlation with the speed of engraftment and hematopoietic reconstitution than their post-thaw counterparts in pediatric recipients, suggesting that it is essential to perform hematopoietic potency assay on each cord blood unit prior to listing or release for administration.