Background. Chemotherapy-induced nausea and vomiting (CINV) is a troublesome side-effect of chemotherapy in pediatric patients undergoing osteosarcoma treatment. In this context, the role of 5-hyd roxytryptamine-3 (5-HT3) receptor antagonists needs to be explored. Objectives. To evaluate the superiority of single-dose palonosetron over granisetron in pediatric patients undergoing highly emetogenic chemotherapy (HEC) for osteosarcoma. Materials and methods, In this double-blind, randomized study, pediatric patients were assessed in terms of acute nausea and vomiting following HEC for osteosarcoma. These children were assigned to group 1 (palonosetron) and group 2 (granisetron) without any other antiemetic prophylaxis. The primary outcome variable was the children's segment with a complete response (CR) during the acute phase of the 1st on-study chemotherapy cycle. The risk factors associated with the emesis were analyzed. The patients were followed up for the first 24 h after chemotherapy. Results. A total number of 200 children were evaluated in terms of the response, and other factors that might alter the response were assessed in the 2 groups. These 200 children underwent 604 blocks of chemotherapy. Complete responses were documented in 83% and 72% of children receiving palonosetron and granisetron, respectively, during the acute phase. Only dexamethasone, used as a rescue medication, was found to be a significant risk factor that predisposed to the response (p < 0.05). Conclusions. Single-dose palonosetron is an effective alternative to granisetron for preventing CINV in children receiving HEC for osteosarcoma.