It is known that the production of free O2 radicals and oxidation products have a significant increase in patients with cancer. There are endogeneous protection systems in order to remove free O2 radicals. One of these endogeneous protection system is carnitine. Carnitine has an important role in muscle functions and in obtaining energy from the membranes of body cells. This study aims to investigate the role of L-carnitine, L-propionyl carnitine and malondialdehyde (MDA) in antioxidant mechanism in children recently diagnosed with solid tumor. The study group were consisted from 57 children from 2 children's cancer centers (Gazi University Pediatrics Department and Sami Ulus Pediatrics Hospital) who were recently diagnosed with solid tumor and 45 healthy control. There was no significant difference in free carnitine and L-propionyl carnitine levels between patients with solid tumor and healthy controls. But, MDA levels were significantly higher in children with recently diagnosed solid tumor than in healthy controls.