Objective: Cancer treatment in children leads to failure to complete the childhood vaccination program and weakening or loss of vaccine-acquired immunity. Post-treatment vaccine responses of children receiving cancer treatment vary. In this study, we aimed to investigate serum antibody status, and vaccine responses in children after cancer treatment. Methods: Pediatric patients who were admitted to Hacettepe University Hospitals between January 1, 2015, and December 31, 2020, who received chemotherapy for lymphoma and solid organ tumors, and whose diseases were in remission were included in the study. Vaccines administered after cancer treatment, hepatitis A (HAV), hepatitis B (HBV), varicella zoster (VZV), measles-mumps-rubella (MMR) serum antibody levels, and changes in vaccine responses after treatment were retrospectively investigated. Results: The study included 533 patients. After treatment, measles, HAV, rubella, HBV, VZV, and mumps, seronegativity were found in 83.5%, 64%, 60.1%48,5%, 43.3%, and 28%of the patients, respectively. Post-treatment rates of antibody loss in descending order were measles (47.1%), HAV (31.9%), HBV (31.4%), mumps (28.6%), VZV (21.7%), and rubella (11.4%). Seroconversion rates to one dose of vaccines in descending order, were (83.6%), rubella (82.9%), HBV (81.4%), VZV (63.5%), mumps (45.4%), and measles (33.3%). Seroconversion rates to two doses of the same vaccines, in descending order, were: HAV (98.8%), VZV (84.6%), rubella (80%), HBV (80%), measles (32.2%), and mumps (36.2%) Conclusion: Serologic vaccine responses of patients after treatment were lower than expected even with repeated doses. As these patients may require intermittent serologic evaluations and repeated vaccinations according to their risk status, we have planned longer-term follow-ups of them.