There are various applications of organosilicon compounds in papermaking. Additionally, organosilicons have been applied to improve the water resistance of some lignocellulosic materials. The performance, however, of such compounds for the hydrophobation of paperboard is unclear. In this study, an organosilicon solution was internally and externally applied to old corrugated container (OCC) paperboard at ambient temperature. Examination of the infrared spectra of treated paperboard confirmed the presence of CH2 groups and hydrophobic organic chains of organosilicon in the treated paperboard. Both internal and external treatment of the paperboard helped its resistance to water, though external treatment was more successful in the late reduction of the contact angle of water droplets and also in reducing water uptake.