Nonporous monodispersed silica spheres of 1.3 mu m. were coated with gold nanoparticles (AuNPs) and subsequently coated with n-octadecanethiol. By transmission electron microscopy analysis, the average diameter of the AuNPs on the silica spheres was determined to be 12 nm. The chromatographic and electrochromatographic properties of self-assembled n-octadecanethiol AuNP-coated silica microspheres (C18-AuNPs-SiO2) were investigated using a group of nonpolar PAHs. The stationary phase appears to display a characteristic reversed-phase behavior. Higher separation efficiency and shorter separation times were obtained using pressurized CEC (pCEC) compared with capillary LC (CLC). A maximum column efficiency of about 2.5 x 10(5) plates per meter and less than 18 min separation time for benzene were obtained in pCEC while only 66 507 plates per meter and an analysis time of nearly 100 min were observed in CLC mode. A chemical stability test of the C18-AuNPs-SiO2 stationary phase under extremely high and low pH conditions demonstrated that it is stable at pH 12 and 1 for at least 60 h. The results confirm that C18-AuNPs-SiO2 possesses a high rigidity to withstand high packing pressures and can be used as a good stationary phase for CLC and pCEC.