Introduction: Osteosarcoma is a malignant neoplasm originating from poorly differentiated cells in the metaphyseal area long bones of children, with a 5-year survival rate below 20%. The evaluation of patient?s prognosis with osteosarcoma using the modified Glasgow Prognostic Score (mGPS) determine the albumin and C-Reactive Protein values to assess inflammation of a tissue. The mGPS scores are 0,1,2 with the higher the score the worse the prognosis. Researchers want to know the role of mGPS in osteosarcoma patients and the prognosis of life expectancy in a general hospital. Material and Method: A retrospective cohort study with a population of osteosarcoma patients at General Hospital H. Adam Malik Medan, which was examined for albumin and C-Reactive Protein (CRP). Using the total sampling method, patients? data was obtained through hospital medical records from January 2012 to December 2017 and a mGPS assessment (0,1,2) was recorded. Then a follow-up was carried out recording patients who were found to survive at >2 years and >5 years. Results: There were 34 patients, of which 26(76%) were male and 8(24%) were female. With the highest age group in the 2nd decade (n=20, 59%) followed by the 3rd decade (n=6, 17%) and the 1st decade (n=5, 15%). The predilection for tumor location was often the same in the distal femur and proximal tibia (n=12, 35%) followed by the proximal humerus (n=5, 15%), and proximal femur (n=4, 12%). Meanwhile, the number of patients based on the mGPS 0-2 value was overal the same (n=11-12, 32-36%). In the 2-year survival rate group (p=0.033), there were 9 (45.0%), 7 (35.0%), and 4 (20.0%) patients with mGPS scores of 0, 1, and 2. Meanwhile, there were 5 (71.4%), 2 (28.6%), and 0 (0.0%) patients with mGPS scores of 0, 1 and 2 in the 5-year survival rate group (p=0.009). Conclusion: Based on the results of data analysis, it was found that there was a significant relationship (p <0.05) between the mGPS assessment and the patient's life expectancy in 2 years and 5 years.