This study aimed to determine the effects of sea buckthorn pulp oil treatment (800 mg/day for 60 days) on inflammatory, systemic oxidative/reductive status and endothelial function, in obese children. A total of 41 obese children (10–18 years old) and thirty controls were enrolled. The measurements were done before and after pulp oil administration. Ultrasounds were used for flow-mediated dilatation (FMD) and carotid artery intima-media thickness (IMT) measurements and colorimetric and ELISA methods for biochemical parameters. In the obese children versus the lean ones, increased oxidative stress (high malonyldialdehyde, high respiratory burst (RB)), low antioxidant defence (low blood glutathione, low TEAC), inflammatory status (high CRP, ceruloplasmin), adipocytokines disturbance (low adiponectin and high leptin), insulin resistance (high fasting C peptide), low FMD (P<0.001), and high IMT (P<0.01) were measured. Treatment reduced total cholesterol (P<0.03), triglycerides (P<0.01), RB (P<0.03), leptin (P<0.049), ceruloplasmin (P<0.01), fasting C peptide (P<0.01), blood pressure (P<0.01), and IMT (P<0.03). In conclusion, sea buckthorn pulp oil treatment prevents atherosclerosis by lowering triglyceridemia, cholesterolemia, and blood pressure (strong effects) and by reducing oxidative stress, inflammation, and insulin resistance (weak effects).