Surface modification of TiO2 nanoparticles with 3-methacrylic acyloxy propyl trimethoxysilane (KH570) was carried out in the liquid phase. The modified TiO2 nanoparticles, as charge control agents (CCAs), were added to toner. Infrared. and X-ray photoelectron spectroscopies provided strong indications of the formation of organic links between the TiO2 and the KH570. The thick coating layer of KH570 deposited on the surface of TiO2 nanoparticles was determined to be about 2-5 nm by transmission electron microscopy. The hydrophobicity of the modified toner decreased when the amount of coated KH570 reached 5.28 wt % and then increased with further increasing amount of coated KH570. The charge-to-mass ratio (Q/M) of the modified toner shifted in the negative direction with increasing amount of coated KH570; however, with increasing amount of modified TiO2, the value of Q/M shifted in the positive direction. The reason for this difference is that the OH groups existing on the surface of TiO2 transferred from the toner to the carrier after friction.