Background. It is suggested that early lymphocyte recovery after chemotherapy are associated with better outcome for patients with cancer. We aimed to determine the prognostic significance of lymphocyte recovery in pediatric patients receiving chemotherapy for osteosarcoma. Methods. We retrospectively reviewed the medical records of 32 patients treated for osteosarcoma at Korea Cancer Center Hospital from May 2002 to March 2016. Patients received chemotherapy comprising high-dose methotrexate (12 g/m2 on day 1, 8), cisplatin (100 mg/2 on day 14) and doxorubicin (30 mg/m2 on day 14 & 15). Neutrophil (ANC 14), lymphocyte (ALC14), and monocyte (AMC14) counts 14 days after the first course of chemotherapy were analyzed for their association with treatment outcomes. Results. The median age of the patients (10 female, 22 male) were 10.2 years (range, 3.2-16.2 years). Tumor sites were distal femur (n=16), proximal humerus (n=7), proximal tibia (n=3), proximal fibula (n=2), and elsewhere (n=4). Five patients had metastasis at the time of diagnosis (lung in 4, lung and bone in 1). At the beginning of chemotherapy, the median values of neutrophil, lymphocyte and monocytes counts were 3,680/µL (range, 1,510-11,020/µL), 2,210/µL (range, 1,290-4,590/µL) and 375/µL (range, 200-1,020/µL), respectively. The median values of ANC14, ALC14 and AMC14 were 520/µL (range, 40-5,470/µL), 1,550/µL (range, 650-2,610/µL) and 330/µL (range, 70-890/µL), respectively. ALC14, AMC 14 and ANC14 were not different according to the disease stage. Patients were followed for a median 67.5 months (range, 4.5-174.7 months), and 5-year overall (OS) and event-free survival (EFS) rates were 57.4±9.4% and 53.0±9.2%, respectively. For the association between ALC14, AMC14 and treatment outcomes, a subset analysis was performed in 27 patients with localized disease. Higher ALC14 (≥ 1,550/µL) was not associated with better survival. However, patients with ALC14/AMC14 ≥ 5.0 (n=15) had better OS than the 12 cases with ALC14/AMC14 5.0 (91.7±8.0% vs. 74.1±13.0%, P=0.047). Conclusions. Our data might be used as a basis to modify clinical trials involving immunotherapy for osteosarcoma. Further studies involving large cohort are necessary to validate our findings.