Background: The prognosis of osteosarcoma is very unsatisfactory due to frequent tumor metastases to the lung or resistance to chemotherapy. A marker is needed to identify the prognosis of patients with osteosarcoma when diagnosed with the aim of being able to receive cancer treatment as soon as possible to improve a better prognosis. Alkaline phosphatase (ALP) and Lactate dehydrogenase (LDH) have potential in assessing the prognosis in osteosarcoma.
 Purpose and Objectives: The researcher wanted to investigate the relationship between preoperative serum ALP and LDH levels on the clinical prognosis of osteosarcoma patients.
 Methods: This research is analytic retrospective with the source of data is medical records and was conducted at the Department of Surgery FK-USU/RSUP Haji Adam Malik Medan with research code of ethics No. 426/KEPK/USU/2022. The subjects of this study were patients with osteosarcoma who were treated at Division of Orthopedic Surgery at Haji Adam Malik Hospital Medan from January 2015-December 2017 who met the inclusion criteria.
 Results: There was no significant relationship between ALP and LDH with five-year survival with p-values of 0.557 and 0.179 (p>0.05). ALP has a weak correlation with five-year survival with an r value of -0.019 which means the higher the ALP, the lower the five-year survival of the patient. Meanwhile, LDH has a weak correlation with an r value of 0.093, which means the higher the LDH, the higher the patient's five-year survival. The ALP value in this study had a median value of 212 U/L and an LDH value of 489 U/L. ALP has sensitivity of 61.1% and specificity of 57.1% with a cut-off of 217.5 U/L. Meanwhile, LDH sensitivity was 61.2% and specificity was 51.4% with a cut-off of 488.5 U/L.
 Conclusion: There is no significant relationship between ALP and LDH with five-year survival.