The synthesis of novel magnetic nanoparticles (MNPs), coated with octadecyl group -modified silica (nano SiO(2)C18) containing carbon nanotubes (CNTs) under supercritical CO2 medium, is reported. Transmission electron micrographs revealed MNPs decorated the surface of the CNTs and nano SiO(2)C18. The hybrid nano particles were used for the determination of five neonicotinoids and four sulfonylureas pesticides at trace levels by HPLC-UV. A comparative study of analyte adsorption and desorption was conducted with similar magnetic composites prepared by high thermal decomposition and sc-CO2 methods. Both sorbents adsorbed the analytes to some extent, but higher recoveries were obtained by using a mixture of both nanomaterials. This mixture was used for the extraction of neonicotinoids and sulfonylureas pesticides from water and fruit juices samples. MNPs can be re -used ten times at least. Detection limits range from 0.07 to 0.60 mu g mL(-1), recoveries from 78 to 95%, and relative standard deviations are < 5%.